Did a deal at Yalta lower the Iron Curtain?

Not on its own. At Yalta, in February 1945, Roosevelt, Churchill and Stalin planned the postwar peace, and the conference promised free elections across liberated Europe. But the promise met a hard fact: the Soviet army had occupied Poland completely and held much of Eastern Europe with military power three times greater than the Allies in the West. Yalta did not lower the Iron Curtain so much as show where the armies already stood.

The famous phrase came later. On 5 March 1946, in Fulton, Missouri, Churchill said that "from Stettin in the Baltic to Trieste in the Adriatic, an iron curtain has descended across the Continent." Stalin answered in the newspaper Pravda that Churchill was a warmonger, and that Soviet friendship with Eastern European states was a safeguard against another invasion.

Churchill did not invent the image, either. Queen Elisabeth of Belgium had used it in 1914 about a divide between her people and Germany, and Goebbels used it in February 1945 to predict a curtain falling over Soviet-controlled territory. At first the term described a literal barrier of razor wire, fences, minefields and watchtowers, and it served to keep people in and information out.