The major global conflict that significantly altered the political landscape in Europe in the 20th century was World War II. The war, fought from 1939 to 1945, led to the collapse of several European empires and the emergence of new political structures, including the United Nations and the Cold War. The aftermath reshaped national borders and ideologies, giving rise to superpowers like the United States and the Soviet Union. Additionally, it prompted movements towards European integration, ultimately contributing to the formation of the European Union and influencing international relations for decades.