Congress would override President Johnson's vetoes. What were they protecting by doing this?

Congress was protecting slaves that were freed after the Civil War

Explanation:

Johnson held that blacks were not qualified to become U.S. citizens and that the measure would “operate in favor of the colored and against the white race.” It was mainly made to protect rights

on april 6, 1917, the u.s. joined its allies--britain, france, and russia--to fight in world war i. under the command of major general john j. pershing, more than 2 million u.s. soldiers fought on battlefields in france.