Throughout his life, Guthrie was associated with United States communist groups, although he did not appear to belong to any. With the outbreak of World War II and the non-aggression pact the Soviet Union had signed with Germany in 1939, the anti-Stalin owners of KFVD radio were not comfortable with Guthrie's political leanings after he wrote a song praising the Molotov–Ribbentrop Pact and the Soviet partition of Poland. He left the station, ending up in New York where he wrote and recorded his 1940 album "Dust Bowl Ballads", based on his experiences during the 1930s, which earned him the nickname the "Dust Bowl Troubadour". In February 1940 he wrote his most famous song, "This Land Is Your Land". He said it was a response to what he felt was the overplaying of Irving Berlin's "God Bless America" on the radio.