Which outcome followed Germany's invasion of Poland regarding the start of World War II?

• A. Poland formed an alliance with Germany
• B. The United States entered the war immediately
• C. The United Nations was established
• D. Britain and France declared war on Germany

Answer: (D)

The key idea is that a major act of aggression by Germany—invading Poland—triggered the defense commitments Britain and France had made to Poland. Because they had guaranteed Poland’s sovereignty, they responded by declaring war on Germany, and this action marks the start of World War II in Europe. The invasion on September 1, 1939, showed that Germany was willing to use force to redraw borders, and Britain and France followed through on their promises, leading to war declarations a couple of days later. The United States did not enter the war immediately, only joining after the attack on Pearl Harbor in 1941, and the United Nations did not exist yet in 1939 (it was established later, in 1945).