A rebel fighter points his weapon at Syrian regime forces in Deir ez-Zor, on Monday, September 2. President Barack Obama has gone to Congress to get approval for possible military intervention in Syria. Tensions in Syria began to flare in March 2011 and escalated into an ongoing civil war. Click through to view the most compelling images taken since the start of the conflict: 
Syrian firefighters try to extinguish a fire after a missile hit a residential building in Damascus, Syria, on September 2. 
A U.N. arms expert collects samples during an inspection of a suspected chemical weapons strike site in the Ghouta area outside Damascus on August 29. 
People search for belongings in rubble in Raqqa, Syria, on August 29. 
Free Syrian Army fighters launch a rocket toward forces loyal to Syrian President Bashar al-Assad in Deir Ezzor on August 29. 
A Syrian Kurd uses hay to hide another woman in a training session organized by the Kurdish Women's Defense Units on Wednesday, August 28, in a northern Syrian border village. They're preparing if the area comes under attack. 
Free Syrian Army fighters escort U.N. vehicles with chemical weapons experts on August 28 through a site of a suspected chemical weapons attack outside Damascus. 
A Free Syrian Army fighter takes position behind sandbags in the old city of Aleppo, Syria, on Tuesday, August 27. 
A U.N. team leaves its Damascus, Syria, hotel in a convoy on Monday, August 26. The team was to investigate an alleged chemical attack that killed hundreds last week in a suburb of the Syrian capital. Sniper fire hit a vehicle used by the U.N. chemical weapons investigation team multiple times Monday, according to the United Nations. 
A Syrian soldier walks down a street in Damascus on Saturday, August 24. 
Pigeons lie dead on the ground on August 24 from after what activists say is the use of chemical weapons by government forces in the Damascus suburb of Arbeen. 
Columns of smoke rise in Barzeh after heavy shelling on Friday, August 23. 
A young Free Syrian Army fighter is reflected in a mirror as he takes position in a house in Aleppo on Thursday, August 22. 
Rebels move around a building in Aleppo on August 22. 
Syrian rebels claim pro-government forces used chemical weapons to kill citizens outside Damascus on Wednesday, August 21. People inspect bodies in this photo released by the Syrian opposition Shaam News Network. 
People search the rubble of a bombed building in Aleppo, Syria, on Friday, August 16. 
Men bury the bodies of six members of the same family killed in a bombing in Raqqa on Saturday, August 10. 
Syrian Army soldiers patrol a devastated street in Homs on Wednesday, July 31. 
Free Syrian Army fighters move through a hole in a wall in Khan al-Assal on Monday, July 22, after seizing the town. 
A rebel fighter walks past swings in a deserted playground in Deir al-Zor, Syria, on Sunday, July 21. 
A rebel fighter speaks with a fellow fighter through a hole in a wall in Deir al-Zor on July 21. 
A Free Syrian Army fighter casts a shadow on a wall as he carries his weapon in a shelter in Deir al-Zor on Thursday, July 18. 
Yahya Sweed, 13, is comforted by his father as he lies on a bed in Kfar Nubul on Tuesday, July 16. The boy was injured by shrapnel, resulting in the amputation of his right leg. 
A rebel fighter naps in a trench about 300 feet from the Syrian government forces' positions along the highway connecting Idlib with Latakia on Monday, July 15. 
A rebel fighter uses a hole in the wall of a destroyed school to aim at Syrian government forces in the Izaa district of Aleppo on Sunday, July 14. 
A Free Syrian Army fighter uses a mirror to scope out snipers loyal to Syrian President Bashar al-Assad in Aleppo on Friday, July 12. 
A Free Syrian Army fighter stands over a boy who was injured during shelling in Al-Bara on Monday, July 8. 
Members of the Free Syrian Army fire a homemade rocket toward regime forces in Deir al-Zor on Sunday, June 16. 
Syrian rebels leave their position in the northwestern town of Maaret al-Numan on Thursday, June 13. The White House said that the Syrian government has crossed a "red line" with its use of chemical weapons and announced it would start arming the rebels. 
Forces loyal to Syrian President Bashar al-Assad are seen near Qusayr on Thursday, May 30. 
Syrian rebels take position in a house during clashes with regime forces in the old city of Aleppo on May 22. 
Syrian army soldiers take control of the village of Western Dumayna north of the rebel-held city of Qusayr on Monday, May 13. Syrian troops captured three villages in Homs province, allowing them to cut supply lines to rebels inside Qusayr town, a military officer told AFP. 
Rebel fighters fire at government forces in the northern Syrian city of Aleppo on Sunday, May 12. 
Searchers use a flashlight as they look for survivors among the rubble created by what activists say was a missile attack from the Syrian regime, in Raqqa province, Syria, on April 25. 
A Kurdish fighter from the "Popular Protection Units" (YPG) takes position inside a building in the majority-Kurdish Sheikh Maqsood area of Aleppo, on Apri. 21. 
People walk past destroyed houses in the northern Syrian town of Azaz on Sunday, April 21. 
Free Syrian Army fighters take positions prior to an offensive against government forces in the Khan al-Assal area, near Aleppo on Saturday, April 20. 
Men inspect damage at a house destroyed in an airstrike in Aleppo on April 15. 
Syrian and Kurdish rebel fighters walk in the Sheikh Maqsud district of Aleppo on April 14. 
A female rebel monitors the movement of Syrian government forces in Aleppo's Sheikh Maqsud neighborhood on Thursday, April 11. 
A rebel runs to avoid sniper fire from Syrian government forces in Aleppo on April 11. 
Syrian rebels observe the movement of Syrian government forces around Al-Kendi hospital in Aleppo on Wednesday, April 10. 
Rescue teams and security forces check out the scene of a deadly car bomb explosion in Damascus on April 8. 
The fighting has taken a toll on buildings in Aleppo's Saladin district, seen here on April 8. 
A Syrian rebel runs for cover in Deir ez-Zor on April 2. 
A rebel checks for snipers across the street toward the Citadel in Aleppo, Syria, on Saturday, March 30, in this photo taken by iReporter Lee Harper. 
A Free Syrian fighter mourns the death of a friend in Aleppo on March 30, in this photo taken by iReporter Lee Harper. 
A Syrian opposition fighter runs for cover from Syrian army snipers in Aleppo on Wednesday, March 27. 
A Syrian girl covers her face to protect herself from fumes as a street covered with uncollected garbage is fumigated in Aleppo on Sunday, March 24. 
A Syrian man and his family drive past damaged buildings in Maarat al-Numan, on Wednesday, March 20. 
Syrians carry the body of a Syrian army soldier during a funeral ceremony in Idlib province on Tuesday, March 19. 
Syrian rebels take position in Aleppo, the largest city in the country, on March 11. 
Syrian men search for their relatives amongst the bodies of civilians executed and dumped in the Quweiq River on March 11. 
A Free Syrian Army fighter looks back as smoke rises during fighting between rebel fighters and forces loyal to Syria's President Bashar al-Assad on the outskirts of Aleppo on Saturday, March 2. 
Residents read Shaam News newspapers published by the Free Syrian Army in Aleppo on March 2. 
A member of the Free Syrian Army reacts to the death of a comrade who was killed in fighting, at Bustan al Qasr cemetery in Aleppo on Friday, March 1. 
A rebel fighter throws a home-made grenade at Syrian government forces in Aleppo on February 16. 
A member of the Free Syrian Army stands with his weapon as he looks at a rainbow in Aleppo on February 16. 
A Syrian woman looks through a bus window in Aleppo on February 14. 
Free Syrian Army fighters walk through a dust-filled stairwell in Damascus on February 7. 
A Syrian rebel gestures at comrades from inside a broken armored personnel carrier in Al-Yaqubia on February 6. 
A rebel fighter throws a hand grenade inside a Syrian Army base in Damascus on February 3. 
People stand in the dust of a building destroyed in an airstrike in Aleppo, Syria on February 3. 
Free Syrian Army fighters run as they enter a Syrian Army base during heavy fighting in the Arabeen neighborhood of Damascus on February 3. 
An unexploded mortar shell fired by the Syrian Army sits lodged in the ground in Damascus on January 25. 
Fighters from Fateh al Sham unit of the Free Syrian Army fire on Syrian Army soldiers at a check point in Damascus on January 20. 
A Free Syrian Army fighter walks between buildings damaged during Syrian Air Force strikes in Damascus on January 19. 
A Syrian rebel fighter tries to locate a government jet fighter in Aleppo on January 18. 
Syrian rebels launch a missile near the Abu Baker brigade in Albab on January 16. 
A Syrian boy walks near rubbish next to tents at a refugee camp near the northern city of Azaz on the Syria-Turkey border, on January 8. 
Syrians look for survivors amid the rubble of a building targeted by a missile in Aleppo on January 7. 
A father reacts after hearing of a shelling by forces loyal to Syria's President Bashar al-Assad in Aleppo on January 3. 
A patient smokes a cigarette at Dar Al-Ajaza psychiatric hospital in Aleppo on December 18, 2012. The psychiatric ward, housing around 60 patients, has lacked the means to function properly since fighting broke out there in July. 
Syrians mourn a fallen rebel fighter at a rebel base in the al-Fardos area of Aleppo on December 8. 
Members of Liwa (Brigade) Salahadin, a Kurdish military unit fighting alongside rebel fighters, monitor the area in the besieged district of Karmel al-Jabl in Aleppo on December 6. 
A member of Liwa Salahadin aims at a regime fighter in the besieged district of Karmel al-Jabl in Aleppo on December 6. 
Two young boys sit underneath a washline in a refugee camp on the border between Syria and Turkey near Azaz on December 5. 
The bodies of three children, who were allegedly killed in a mortar shell attack that landed close to a bakery in Aleppo, on December 2, are laid out for identification by family members at a makeshift hospital at an undisclosed location of the city. 
Smoke rises in the Hanano and Bustan al-Basha districts in Aleppo on December 1 as fighting continues through the night. 
Damaged houses in Aleppo are seen after an airstrike on November 29. 
A Syrian rebel mourns the death of a comrade in Maraat al-Numan on November 20. 
Syrians protesters stand on Assad's portrait during an anti-regime demonstration in Aleppo on November 16. 
A Syrian rebel takes cover during fighting against Syrian government forces in Aleppo on November 15. 
Syrian opposition fighter Bazel Araj, 19, sleeps next to his pistol in Aleppo on November 11. 
A rebel fighter fires at a Syrian government position in Aleppo on November 6. 
A Syrian rebel leaps over debris left in the street while running across a "sniper alley" near the Salahudeen district in Aleppo on November 4. 
Rebels hold their position in the midst of a battle on November 3 in Aleppo. 
A man cries while being treated in a local hospital in a rebel-controlled area of Aleppo on October 31. 
A man is treated for wounds after a government jet attacked the Karm al-Aser neighborhood in eastern Aleppo on October 31. 
A Syrian rebel interrogates a handcuffed and blindfolded man suspected of being a pro-regime militiaman in Aleppo on October 26. 
Smoke rises from a fuel station following a mortar attack as Syrian women walk on a rainy day in the Arqub neighborhood of Aleppo on October 25. 
A Syrian rebel fires at an army position in the Karm al-Jabal district of Aleppo on October 22. 
A wounded Syrian boy sits on the back of a truck carrying victims and wounded people to a hospital following an attack by regime forces in Aleppo on October 21. 
A man lies on the ground after being shot by a sniper for a second time as he waits to be rescued by members of the Al-Baraa Bin Malek Battalion, part of the Free Syria Army's Al-Fatah brigade, in Aleppo on October 20. 
Syrian army soldiers run for cover during clashes with rebel fighters at Karam al-Jabal neighborhood of Aleppo on October 20. 
Smoke rises after a Syrian Air Force fighter jet fired missiles at the suburbs of the northern province of Idlib on October 16. 
A Syrian opposition fighter stands near a post in Aleppo on October 11. 
A Syrian man mourns the death of his father, who was killed during a government attack in Aleppo on October 10. 
A rebel fighter is carried by his friends and laid on a gurney to be treated for gunshot wounds sustained during heavy battles with government forces in Aleppo on October 1. 
Syrian rebels help a wounded comrade to an Aleppo hospital after he was injured in a Syrian army strike on September 18. 
Free Syria Army fighters are reflected in a mirror they use to see a Syrian Army post only 50 meters away in Aleppo on September 16. 
A Syrian man carrying grocery bags tries to dodge sniper fire as he runs through an alley near a checkpoint manned by the Free Syria Army in Aleppo on September 14. 
A woman walks past a destroyed building in Aleppo on September 13. 
Free Syrian Army fighters battle during street fighting against Syrian army soldiers in Aleppo on September 8. 
A Syrian man wounded by shelling sits on a chair outside a closed shop in Aleppo on September 4. 
A woman sits in her wheelchair next to her house, damaged by a Syrian air raid, near Homs on August 26. 
Members of the Free Syrian Army clash with Syrian army soliders in Aleppo's Saif al-Dawla district on August 22. 
A man mourns in front of a field hospital on August 21 in Aleppo. 
Wounded civilians wait in a field hospital after an air strike on August 21 in Aleppo. 
People pray during the funeral of a Free Syrian Army fighter, Amar Ali Amero, on August 21. 
A man cries near the graves of his two children killed during a recent Syrian airstrike in Azaz on August 20. 
A Syrian woman holds her dead baby as she screams upon seeing her husband's body being covered following an airstrike by regime forces on the town of Azaz on August 15. 
A Syrian rebel runs in a street of Selehattin during an attack on the municipal building on July 23. 
Syrian rebels hunt for snipers after attacking the municipality building in the city center of Selehattin on July 23. 
Members of the Free Syrian Army's Mugaweer (commandos) Brigade pay their respects in a cemetery on May 12 in Qusayr. 
Syrian rebels take position near Qusayr on May 10. 
A Free Syrian Army member takes cover in underground caves in Sarmin on April 9. 
Rebels prepare to engage government tanks that advanced into Saraquib on April 9. 
Men say prayers during a ceremony in Binnish on April 9. 
A young boy plays with a toy gun in Binnish on April 9. 
A Free Syrian Army rebel mounts his horse in the Al-Shatouria village near the Turkish border in northwestern Syria on March 16, a year after the uprising began. 
Syrian refugees walk across a field before crossing into Turkey on March 14. 
A rebel takes position in Al-Qsair on January 27. 
A protester in Homs throws a tear gas bomb back towards security forces, on December 27, 2011. 
A man stands under a giant Syrian flag outside the Umayyad Mosque in Damascus on December 24, 2011. 
A member of the Free Syrian Army looks out over a valley in the village of Ain al-Baida on December 15, 2011. 
Members of the Free Syrian Army stand in an valley near the village of Ain al-Baida, close to the Turkish border, on December 15, 2011. 
Displaced Syrian refugees walk through an orchard adjacent to Syria's northern border with Turkey on June 14, 2011, near Khirbet al-Jouz. 
A Syrian man holds up a portrait of President Bashar al-Assad during a rally to show support for the president in Damascus on April 30, 2011. 
Syrians rally to show their support for President Bashar al-Assad in Damascus on April 30, 2011. 
A screen grab from YouTube shows thick smoke rising above as Syrian anti-government protesters demonstrate in Moaret Al-Noman on April 29, 2011. 
A screen grab from YouTube shows Syrian anti-government protesters run for cover from tear gas fired by security forces in Damascus on April 29, 2011, during the "Day of Rage" demonstrations called by activists to put pressure on al-Assad. 
Syrians wave their national flag and hold portraits of al-Assad during a rally to show their support for their leader in Damascus on March 29, 2011. 
A woman sits by the hospital bed of a man allegedly injured when an armed group seized rooftops in Latakia on March 27, 2011, and opened fire at passers-by, citizens and security forces personnel according to official sources. 
Syrian protesters chant slogans in support of al-Assad during a rally in Damascus on March 25, 2011. 
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(CNN) -- The White House has been working overtime this week, trying to line up votes from skeptical lawmakers for a military strike on Syria. The maneuverings began over the weekend when President Barack Obama asked Congress to approve an attack on Syrian targets, saying it's the right thing to do after the regime allegedly used chemical weapons against rebel strongholds.
There are so many moving parts to this complicated story that it can become quite difficult to keep up.
As you begin your first day back at work after the long holiday weekend, let this Q&A bring you up to speed on the dizzying developments.
1. Give me a quick recap first. What does the White House want?
The White House stance is this: The Assad regime used chemical weapons in a Damascus suburb last month. That's against international law, and there has to be consequences. It held a classified briefing Sunday to make its case to about 100 House and Senate members. But one after another, lawmakers emerged supremely unconvinced. So it's got its work cut out.
2. What happens next?
Congress doesn't officially come back until September 9. That buys the White House a little time. And it intends to spend the rest of this week trying to win the skeptics over. The White House will hold classified briefings nearly every day this week. The president's meeting with House Speaker John Boehner and Minority Leader Nancy Pelosi on Tuesday. And there are House and Senate committee hearings scheduled.
3. Why do lawmakers need convincing?
Lawmakers agree that Syrian President Bashar al-Assad's alleged use of chemical weapons is a travesty. But they also don't want a repeat of Iraq. So, they want the administration to really nail their case. "There will be a real questioning as to the veracity of the evidence and if this really happened or not," House Armed Services Chairman Buck McKeon, R-California, told CNN.
4. So, do we have the proof?
Secretary of State John Kerry told CNN's "State of the Union" that blood and hair samples taken from medics point to the nerve agent sarin. But U.N. inspectors who were on the ground investigating the alleged attack could take three weeks to analyze the evidence. And even then, they'll only say if there was a chemical attack, not who was behind it.
5. Are there other reasons giving lawmakers pause?
There are almost as many reasons as there are lawmakers. Some say that what Obama's asking for is too broad. Others want a firm expiration date on American action. Some, like Republican Sen. Ted Cruz, say the U.S. should act only if there's a clear threat to its national security. Others, like Democratic Rep. Janice Hahn, want to know how much it's going to cost taxpayers.
6. Is the White House addressing those concerns?
Yes. Two top Democrats are working to narrow the scope of what Obama asked for. They've also said they'll couple strikes with increased support for the rebels. That seems to have appeased Republican senators John McCain and Lindsey Graham who've said said airstrikes won't go far enough.
7. Will Congress come through in the end?
Obama might be able to count on the Senate, where the Democrats hold a slim majority. The question is, will the Republican-dominated House go along? McCain says that if Congress rejects Obama's call, that would be catastrophic. "It would undermine the credibility of the United States of America and the president of the United States," McCain said. "None of us want that."
8. But Obama doesn't really have to wait for the green light, does he?
Technically, no. The 1973 War Powers Act allows the president to launch military action, but he must notify Congress within 48 hours. But just because he can doesn't mean he will, he says.
9. Even with Congress' blessing, isn't Obama still flouting international law?
Yes. The U.N. charter generally doesn't allow countries to attack other nations unless in self defense or with approval from the Security Council.
10. Why not just go to the Security Council then?
Because any call to action against Syria will most certainly be vetoed by its two allies, Russia and China -- both of whom have veto power.
11. Why are Russia and China against intervention?
Russia says it doesn't buy the U.S. claim. "When we ask for more detailed evidence, they say, 'You know, it's all secret, so we can't show you," Foreign Minister Sergey Lavrov said. "That means that there are no such facts." China says it's against anyone taking unilateral action. Each has its reason: Russia's a big trading partner. And China had has its own share of international controversies over its policies with Tibet as well as allegations of human rights violations.
12. What about our allies?
France is on board, but has said it won't act without the United States as a partner. Britain's hamstrung after its lawmakers voted down Prime Minister David Cameron's call for intervention. And NATO's stance is that while the August 21 attack calls for a "firm international response," it won't come from the alliance itself. "It is for individual nations to decide how to react," it says.
13. Who can we count on?
Turkey, Saudi Arabia and the United Arab Emirates are on board, Kerry says. He expects others to join.
14. What does Syria think about all this?
Al-Assad's been clear: The Middle East is a powder keg; attack Syria and risk a regional war. "Everyone will lose control of the situation when the powder keg explodes," he told the French newspaper Le Figaro. His regime's repeatedly said it didn't use chemical weapons in the August 21 attack. It says jihadists fighting alongside Syrian rebels used them to turn global sentiment against the regime.
15. Can we really afford to wait?
Gen. Martin Dempsey, the chairman of the joint chiefs of staff, says it's fine to wait. A delay won't jeopardize a military strike, he told the president, according to officials
16. What does the Syrian opposition think of that?
Opposition groups want action -- and want it now. And with good reason. There's been no pause in killing: 100,000 and climbing. And on Tuesday, the U.N. refugee agency offered up this grim stat: The number of Syrians who've fled the country has now risen above 2 million. Put another way, every 15 seconds, a Syrian becomes a refugee.
17. How exactly would the U.S. carry out an attack?
No one is calling for boots on the ground. The U.S. would use U.S. warships with Tomahawk cruise missiles. The Tomahawk has a range of about 1,000 miles. It can loiter over targets, circling for hours, and can be reprogrammed midflight to change course. Yes, each costs about $1.2 million, but they can be fired from quite a distance. This means no one has to get within range of Syrian fire.
18. What about civilian deaths?
Dempsey says collateral damage from a strike will be low. But lawmakers say there's no way he could know that.
19. Could Syria strike back?
Syria has some anti-ship missiles -- but they have a range of only 62 to 186 miles, says Edward Hunt, a senior analyst at IHS Jane's. It also has a number of Scuds and similar surface-to-surface weapons, but these are not designed to be used against moving targets such as U.S. warships, Hunt said.
20. What about our military leaders? What do they think?
They have concerns. Dempsey says that even a limited involvement will probably lead to an extended stay. "Deeper involvement is hard to avoid," he wrote to Congress over the summer.
CNN's Matt Smith, Laura Smith-Spark, Jethro Mullen, Elise Labott, Leigh Ann Caldwell, Tom Cohen, Evan Perez, Barbara Starr, Jennifer Rizzo, Dana Bash, David McKenzie, Ashley Killough and Sarah Chiplin contributed to this report.
