Final answer:
The year 1939 was significant as it marked the beginning of World War II with the German invasion of Poland. This event led to larger global conflicts and changed the course of history, influencing America's transition from an isolationist stance to active participation in the war following the Japanese attack on Pearl Harbor in 1942 so the correct answer is option (d)
Step-by-step explanation:
The year 1939 marked the beginning of World War II when Nazi Germany invaded Poland. This marked a significant turning point in world history as it led to a global conflict involving major world powers. The Great Depression, which began in 1929, had largely impacted the political and economic climate preceding the war, and by 1939, countries were inevitably moving toward greater conflict. Although the Japanese attack on Pearl Harbor on December 7, 1942, and the D-Day invasion of France in June 1944 were also pivotal events, they occurred after the official start of World War II. The attack on Pearl Harbor, particularly, was the catalyst for America's entrance into the war, abandoning its isolationist policies.
Each historical perspective on when World War II began is informed by regional emphasis, as Asian historians often cite the Japanese invasion of China in 1937, while Western European and US textbooks typically acknowledge the 1939 invasion of Poland by Germany as the conflict's official commencement. These perspectives highlight the complexities and global aspects of the war which reshaped the twentieth century. The period between World War I and World War II was significant in American history, with developments in immigration, industrialization, technology, and the growth of modern cities.