At the time of hitler's 1939 invasion of poland the us had policy of

During that time the us was not in the war and was practicing a policy of isolationism(as we didn't enter the war till December 7th 1942). Contrary to the policy we were practicing, we were allowing European powers that we were in close relationships with to buy war tools from us. When they could not afford to pay cash we bartered for military bases across the world, and when they could not do that we adopted the policy of lend lease, which is often compared to "letting someone borrow a piece of chewing gum that they promise to return after they use it)

The answer is monsoons.