What happened in the us in the early 1950s?

Apex plz i’m almost done if i get this all right

What pact signed on 1949 reinforce that the united states would not return to an isolationist policy

Which of the following led to a continuation of the treatment in the excerpt above? a)the brutality of the trans-atlantic african slave trade. b)spanish repression after violent native uprisings in new spain during the 16th century. c)european competition to quickly establish colonial holdings in the new world. d)the reliance of the spanish on native americans to provide labor under the encomienda system.