Final answer:
Winston Churchill coined the term "iron curtain" in a speech in 1946 to describe the division between Western capitalist democracies and Eastern Communist states influenced by the Soviet Union, which marked the onset of the Cold War.
Step-by-step explanation:
The world leader who warned of an "iron curtain" descending across Europe after World War II was Sir Winston Churchill. He made this declaration during a speech in Fulton, Missouri, in March 1946, indicating the division of Europe into capitalist democracies in the West and Communist states under Soviet influence in the East.
This metaphor effectively captured the geopolitical reality of post-war Europe and the beginning of the Cold War era. Churchill's speech is historically significant as it highlighted the ideological conflicts between the United States and the Soviet Union, which would dominate global relations for the latter half of the 20th century. The term "iron curtain" came to define the strict boundary that separated Eastern and Western Europe until the end of the Cold War in 1991.