President Barack Obama speaks with Ghanaian President John Atta-Mills at Osu Castle, the government headquarters and a former slave trading fort, in Accra, Ghana, on July 11, 2009. 
President George W. Bush meets women and children at the reproduction and child health unit of Meru District Hospital in Arusha, Tanzania, on February 18, 2008. 
President Bush holds the tusk of an elephant while touring the Mokolodi Nature Reserve in Gaborone, Botswana, on July 10, 2003. 
President Bill Clinton reaches out to shake hands while touring Ushafa, Nigeria, on August 27, 2000. 
President Clinton greets people during a tour of a village in Senegal on April 1, 1998. 
President George H. W. Bush meets people at a displaced persons camp in Mogadishu, Somalia, on December 31, 1992. 
Former Egyptian President Hosni Mubarak and President George H.W. Bush stand together at a ceremony in Cairo, Egypt, on November 24, 1990. 
Left to right, President Jimmy Carter and wife Rosalynn, Egyptian President Anwar Sadat and wife pose in front of the Giza pyramids in Egypt, in March 1979. 
President Richard Nixon and Egyptian President Anwar Sadat greet people in Egypt, in June 1974. - His visit will take him to Senegal, South Africa and Tanzania
- It aims to bolster investment opportunities and promote democracy
- It is his second visit to sub-Saharan Africa as president
- He visited Ghana during his first term in July 2009.
(CNN) -- President Barack Obama flies across the Atlantic on Wednesday for a trip that takes him to Senegal, South Africa and Tanzania, his second visit to sub-Saharan Africa since taking office.
The trip aims to bolster investment opportunities for U.S. businesses, address development issues such as food security and health, and promote democracy.
It comes as China aggressively engages the continent. The Asian nation is pouring billions of dollars into Africa, running oil and mining firms, and replaced the United States in 2009 as the largest trading partner.
Obama's predecessor, George W. Bush, will be in Africa at the same time.
Bush has made multiple visits to Africa since leaving office, and will be in Zambia next week, where he's working with his global health initiative to renovate a cervical cancer screening and treatment center.
While the 44th and 43rd president are not scheduled to meet, first lady Michelle Obama and her predecessor, Laura Bush, will attend the African First Ladies Summit in Tanzania on July 2.
The whole world prays for one man 
Dozens gather to pray for Nelson Mandela Obama's trip is being overshadowed by the declining health of South Africa's revered former president, Nelson Mandela, who is in critical condition at a Pretoria hospital.
Mandela, who emerged from prison after 27 years to lead South Africa out of its dark days of apartheid, is considered the father of modern day South Africa.
Obama will be in Senegal Thursday and Friday. He arrives in South Africa on Saturday, where he will spend the weekend taking part in a host of activities, including meeting with the nation's leaders and visiting Robben Island, where Mandela spent a majority of his prison term.
He will spend Monday and Tuesday in Tanzania, and is expected back in Washington on July 3.
The president made a brief trip to Ghana during his first term in July 2009.
CNN's Kevin Bohn and Ashley Killough contributed to this report.
