Obama, the first black U.S. president, spoke to thousands of marchers on Washington's National Mall on Wednesday to commemorate King's landmark address, which came to symbolize the struggle for equality among blacks and whites in America.
Obama said King's speech inspired millions of Americans to fight for a more just society and rights that people now take for granted.
"To dismiss the magnitude of this progress, to suggest, as some sometimes do, that little has changed, that dishonors the courage, the sacrifice of those who paid the price to march in those years," Obama said.
