What issue was a major disagreement at the Yalta Conference?

The major disagreement at the Yalta Conference centered around Poland's border changes. The leaders, including Franklin D. Roosevelt, Winston Churchill, and Joseph Stalin, debated the future of Poland as it had been significantly affected by World War II and occupied by Soviet forces. Stalin sought to expand Soviet influence in Eastern Europe, which included moving Poland's borders westward, thereby shifting a significant population and altering the power dynamics in the region.

Churchill and Roosevelt were concerned that these changes would compromise the sovereignty of Poland and lead to increased Soviet control over Eastern Europe, contrasting with their vision of self-determination for countries affected by the war. This disagreement highlighted the differing approaches of the Western Allies and the Soviet Union regarding post-war Europe and foreshadowed future tensions in the Cold War.

The other options, such as the formation of NATO, reparations for Germany, and the establishment of the United Nations, were not primary subjects of contention at Yalta. While these issues were important in the broader context of post-war planning, it was the fate of Poland that became a focal point of conflict among the Allied leaders at the conference.