Amajor reason for the united states neutrality in the 1930s was the nation's
a. belief in the domino theory.
b. disillusionment resulting from world war i.
c. strong approval of political conditions in europe.
d. military and naval superiority.

A major reason for the United States neutrality in 1930s was the nation's disillusionment resulting from World War I. The correct option among all the options given in the question is option "b". The people of united States of America was not ready to digest the consequences of another war. The country was going through a time of depression and added pressure would crumble the economy totally.

The rest don't make sense so i say the first one.

Their worse are not meaningful;