What phrase does churchill use to describe soviet power in eastern europe? why might this scare an american audience in 1946?

Churchill use the phrase "Iron Curtain" to describe soviet power in Eastern Europe. He meant that the Soviet Union had separated the Eastern European countries from the West so that no one knew what was going on. He used the word "iron" to signify that it was indestructible.

Churchill’s speech asserting that an Iron curtain had come across Europe might scare the American audience because it was perceived as a declaration of war.