Final answer:
At the Potsdam Conference in July 1945, the American President in attendance was Harry S. Truman. Truman, alongside other Allied leaders, focused on post-WWII reconstruction and discussed the division of Germany and Berlin into sectors as well as the dismantling of Germany's heavy industry.
Step-by-step explanation:
The Potsdam Conference of July 1945
The Potsdam Convention, an important gathering for the discussion of post-World War II arrangements in Europe, took place from July 17th to August 2nd, 1945. The American President who attended the conference was Harry S. Truman. Truman had recently become President after the death of Franklin Roosevelt in April of that year. Alongside Soviet Premier Joseph Stalin and initially Winston Churchill followed by newly elected British Prime Minister Clement Attlee, they discussed significant issues such as the reconstruction of Europe and the division of Germany and Berlin into sectors controlled by the American, British, French, and Soviet forces.
At the conference, Truman was already concerned about Soviet actions in Europe and opposed the heavy reparations Stalin aimed to impose on Germany. Truman's stance was influenced by the desire to avoid a repetition of the cycle of rearmament and aggression that had occurred after World War I. The decisions made at the Potsdam Conference set the stage for the geopolitical landscape of the post-war world.
Notable at the conference was the change in leadership among the Allies, with Truman and Attlee replacing their predecessors who had been part of previous major summits such as Yalta. The significance of these discussions is marked by the presence of leaders of the victorious Allies, setting the policies for post-war recovery.