WASHINGTON (AP) ― Though noting persistent challenges, President Barack Obama heralded Africa as a continent on the rise and a growth market for U.S. businesses as he closed an unprecedented summit Wednesday aimed in part at fostering his own African legacy.

The summit also marked a rare return to Washington for former President George W. Bush, who launched a $15 billion HIV/AIDS initiative while in office and has made public health issues in Africa a priority since leaving the White House. Bush partnered with first lady Michelle Obama to host a daylong event for spouses of the African leaders.

“There’s not many things that convince me to come back to Washington,” said Bush, who now lives in Dallas and steers clear of politics. “The first lady’s summit, of course, is one.”

While Obama has continued Bush’s signature AIDS program, he has also been seeking his own legacy-building Africa initiatives. This week’s U.S.-Africa summit, which brought together leaders from more than 50 African nations, was seen as a cornerstone of that effort and Obama pledged to make the gathering a recurring event. 

“Africa must know that they will always have a strong and reliable partner in the United States of America,” Obama said at a news conference marking the end of the three-day summit.

Much of the summit centered on boosting U.S. business ties with Africa, which is home to six of the world’s 10 fastest-growing economies and a rapidly expanding middle class.

Yet the summit’s final day of discussions underscored the challenges that could undermine that economic growth. Health crises remain among Africa’s most pressing problems, including the current outbreak of the deadly Ebola virus in West Africa.

Obama acknowledged that the public health systems in affected countries have been overwhelmed by the outbreak and said the U.S. was encouraging them to focus their efforts on rapidly identifying and isolating patients.

The president also pledged to expand security cooperation with African nations in order to address threats from terrorism and human trafficking, alluding to U.S. concerns that extremism in North Africa and the Sahel could destabilize the already volatile region.

“The entire world has a stake in the success of peacekeeping in Africa,” Obama said.

Before taking questions from reporters, Obama convened a session with African leaders on good governance, universal rights and the strengthening of civil societies. And he defended U.S. engagement with countries that have problematic records on those fronts, arguing that America’s involvement can help spur those nations to do better.

“We find that in some cases, engaging a country that generally is a good partner but is not performing optimally when it comes to all the various categories of human rights, that we can be effective in working with them on certain areas and criticizing them and trying to elicit improvements in other areas,” Obama said.

Among the leaders treated to an elaborate reception the night before at the White House were figures such as Kenyan President Uhuru Kenyatta, who has pleaded innocent regarding his alleged role in organizing violence that left more than 1,000 people dead. Obama has also spoken out repeatedly against recent laws passed in some African countries targeting lesbians and gays, including Uganda, which was represented at the summit.

As Obama participated in summit meetings, his wife convened a gathering of African first ladies, talking about investments in education, health and economic development. She was joined by Laura Bush, reprising an event the two American first ladies held last summer in Tanzania.

Calling Africa “an underappreciated continent,” Mrs. Obama said it was incumbent upon the world to develop a better understanding of what it has to offer.

“This is the beginning of a lot of work that needs to be done,” she said.

Mrs. Obama and Mrs. Bush also focused on the need to educate girls. Mrs. Obama noted that 30 million girls in sub-Saharan Africa do not attend school.

“We do need to make sure worldwide that all humans are valued,” Mrs. Bush said during the rare joint appearance that highlighted the relationship that has developed between the two first ladies.

George Bush also gave his endorsement for efforts to support women in Africa, declaring, “Taking care of women is good politics.” He announced that a global health partnership that helped screen more than 100,000 women in Botswana, Tanzania and Zambia for cervical cancer in the past three years was expanding into Namibia and Ethiopia

The effort is part of Bush’s “Pink Ribbon Red Ribbon” women’s health initiative that has been a focus of his post-presidency. He has made frequent trips to Africa since leaving the White House, but he rarely visits Washington and weighs in on political debates even less.

A focus on Africa has brought Obama and Bush together in the past. After a scheduling coincidence put them in Tanzania at the same time last summer, they met and laid a wreath in honor of victims of the 1998 U.S. Embassy bombing. Bush and his wife also traveled with the Obamas on Air Force One to South Africa in December for a memorial service honoring South African President Nelson Mandela.

The White House said Obama and Bush did not meet while the former president was in Washington Wednesday.