African Americans were taken from their homes and forced into slavery. Eventually, the term "chattel slave" became coined which means a slave who will be enslaved forever as well as any of his or her descendants (children, children's children, etc.). Due to the European colonization, they no longer had any freedom or life to call their own. Instead, they were forced into labor under harsh conditions for the benefit of their master.
Hitler's power was not checked when the US entered the war. The war with the US was between them and Japan. The USSR did join sides with the allies when Germany broke an treaty. However, the US did win the war between Japan.
