Explain the irony involved in the spanish american war that embittered some black people

The soldiers of the 9th and 10th were not green recruits. They had fought for the Union as members of the U.S. Colored Troops.They were black units staffed with white officers. A few years later, they were joined by two infantry units, the 24th and 25th.These were also made up by black soldiers. For the next two decades, the four units served in the American West. (www.cacsk12.org)