WASHINGTON — President Obama is gathering nearly 50 African heads of state in Washington for an unprecedented summit aimed in part at building his legacy on a continent where his commitment has been questioned.

In contrast to his predecessor, George W. Bush, who launched a $15 billion program to address HIV and AIDS, Obama seems to be lacking a signature Africa initiative.

But the backdrop for the conference that begins Monday underscores what has been a constant challenge to that effort.

Even as Obama immerses himself in talks on regional security, democracy building and business investment in Africa, the world’s attention – and much of his own – will be on an extraordinary array of urgent overseas crises that have erupted.

Among them: Gaza clashes, Russia’s provocations in Ukraine and mounting extremism in Iraq, to name just a few.

An outbreak of the deadly Ebola virus in West Africa also threatens to cast a shadow over the summit, with leaders from at least two affected countries canceling plans to travel to Washington and the U.S. setting up medical screenings for other officials arriving from those nations.

White House officials say the American interests in Africa are immense.

The continent is home to some of the world’s fastest growing economies and a rapidly expanding middle class. The U.S. is also competing for those consumers with China, which surpassed the United States in 2009 as Africa’s largest trading partner.

“The importance of this for America needs to be understood,” Obama said Friday.

“Africa is growing, and you’ve got thriving markets and you’ve got entrepreneurs and extraordinary talent among the people there.”