During which decade did the us pursue a policy for isolation

the 1930s
Explanation: The USA watched carefully the rise of fascism in Europe and Japanese expansion in Asia, but did not intervene, There was a strong isolationist lobby and many had sympathy with both Hitler and Mussolini who they saw as leaders who were putting to rights, the problems of their countries, and were also important bulwarks against communism.
It took the Japanese attack on Pearl Harbour to bring the USA into the war and even then there was no guarantee they would have become directly involved in the conflict in Europe. It was Hitler who declare war on the USA in support of his Japanese Axis allies.