Why is a black president a big deal?
Barack Obama's made history as America's first black president, but why's it such a big deal he's got the top job?
In the 17th and 18th centuries hundreds of thousands of Africans were sold into slavery in America and made to work on cotton and tobacco plantations.
In 1865 slavery was abolished, but black people still didn't have equal rights and had to go to separate schools, churches, and even had to play on different footie teams.
In 1955, a woman, Rosa Parks, sparked protests by refusing to give up her bus seat to a white man - which was against the law at the time.
The protests were led by this man, Martin Luther King, who said he had a dream that one day black and white people in America would be able to come together as equals.
In 1964 the country made a huge leap forward with the introduction of the 1964 Civil Rights Act, which made it illegal to treat people differently because of their race.
But until now, the top job has always gone to a white man, so it's a huge deal for America, and the rest of the world, that Barack Obama has become president.