The General Assembly is considered the highest decision-making body of the United Nations because it is composed of representatives from all member states, providing each member state with an equal vote regardless of its size or power. It serves as a forum for discussing and making decisions on a wide range of international issues, including peace and security, development, human rights, and international law. While the Security Council has significant powers related to peace and security, its authority is limited to those specific areas, whereas the General Assembly has a broader mandate encompassing all aspects of the UN's work.
While the United Nations Security Council is often considered the most powerful body due to its ability to authorize military action and impose sanctions, it is important to note that the Security Council's decisions are ultimately subject to the approval of the General Assembly.
The Treaty of Potsdam ended World War II. It was signed in 1945 between the Allied powers and Germany. The Treaty of Paris came later, in 1947, and dealt specifically with the post-war settlement for Italy.