When did the iron curtain become a metaphor?

The term "Iron Curtain" became a metaphor during the early stages of the Cold War, particularly after Winston Churchill's speech on March 5, 1946, in Fulton, Missouri, where he used it to describe the division between Western democracies and Eastern communist countries. This metaphor symbolized the ideological and physical boundary that separated the Soviet bloc from the West, highlighting the geopolitical tensions and the lack of communication and cooperation between the two sides. The Iron Curtain came to represent the broader conflict between capitalism and communism that characterized much of the 20th century.