Half a century ago black people in the United States often suffered discrimination. Today there is a black President in the White House. But despite all the hard work Obama personally put into achieving this, he wouldn't have become President without the efforts of Americans, of all races, who recognised injustice and were determined to put things right. Martin Luther King was not alone, and he was by no means the first.
In 1996 Obama was a Democratic Party candidate in a local election. He was sent a questionnaire to find out his views on LGBT issues, and replied in an unequivocal way. Amongst his promises was to support same-sex marriages and "fight efforts to prohibit such marriages." In the 2008 Presidential election campaign, however, his stance was somewhat less positive. In fact he had reversed his 1996 position. A month before the Presidential election, his running mate, Joe Biden, was asked if he supported gay marriage. The answer was: "No. Barack Obama nor I support redefining, from a civil side, what constitutes marriage. We do not support that." (YouTube video)
A significant figure in the struggle for equality, and a friend of Martin Luther King, was Bayard Rustin. Towards the end of his life, Rustin came to believe that the gay community was a barometer of human rights - it was, he said, "the community which is most easily mistreated." (blog 3 February 2007)
Since becoming president last week, Obama has put a statement of his civil rights beliefs and policies on the White House website. Much of what he says looks encouraging.
Newsround Blog will be marking UK LGBT History Month, which begins in just a few days.