Many left wingers did not believe W.W.2. was an anti-fascist war; some changed their minds when the Soviet Union was invaded, some didn't.
Harry Pollitt, Secretary of the British Communist Party, resigned over the issue.
My old man went off to fight fascists in Spain, was wounded and imprisoned there. He returned to find he had not only been excommunicated from his church for doing so, but had been given a police record as being a "premature anti-Fascist", which caused him to become blacklisted from his job and the only way he had open to him to earn a living was to become a navvy. My mother, sister and I didn't really get to know him until he finally managed to return home in the mid-fifties.
America (often referred to when I was young as "the late United States") came into the war.... when exactly?
Easy to be smugly simplistic 60 odd years after the event over something that was a little more complicated than it appears at this distance.
Jim Carroll

"Guthrie believed performing his anti-fascist songs and poems at home was the best use of his talents; Guthrie lobbied the United States Army to accept him as a USO performer instead of conscripting him as a soldier in the draft. When Guthrie's attempts failed, his friends Cisco Houston and Jim Longhi pressured Guthrie to join the U.S. Merchant Marine. Guthrie followed their advice: he served as a mess man and dishwasher and frequently sang for the crew and troops to buoy their spirits on transatlantic voyages. Guthrie made attempts to write about his experience in the Merchant Marine but was never satisfied with the results. Longhi later wrote about these experiences in his book Woody, Cisco and Me.] The book offers a rare first-hand account of Guthrie during his Merchant Marine service. In 1945, Guthrie's association with Communism made him ineligible for further service in the Merchant Marine, and he was drafted into the U.S. Army"