The US tried to help in stopping totalitarian aggression without getting fully involved by implementing the Lend Lease Act. The Lend Lease Act was a law that allowed the US government to give financial assistance along with military weapons/resources to countries that were fighting against totalitarian governments like the one established in Nazi Germany.
The goal of this was to help stop the spread of reign like Hitler but this was also supposed to help the US maintain their policy of isolationism (aka not getting involved in other countries affairs).