Before the United States engaged in World War II, the government used a program called lend-lease to provide military and food aid to the Allies. Under lend-lease, the U.S. sent ammunition, tanks, and other supplies overseas.
A lend-lease program involves lending goods with the understanding that they will be used to benefit the donor in some way (or sometimes, that they will eventually be returned). In World War II's lend-lease program, the U.S. gave supplies and material to several Allied nations, and in return those countries defended America from the Axis forces. It was also an indirect way for the U.S. to involve itself in the war before fully committing to fighting with the Allies.