Final answer:
During the 1948 Democratic National Convention, Truman encountered internal party conflict due to his civil rights agenda.
Step-by-step explanation:
Harry S. Truman spoke at the national convention when he was renominated by the Democratic Party for the presidential election. Although the specific question about when Truman spoke is not explicitly answered in the provided material, it's known that during the 1948 Democratic National Convention, Truman faced opposition from the Dixiecrats due to his strong stance on civil rights. This was a significant event as it highlighted a shift in the political dynamics within the Democratic Party and had implications for the election that year.