Answer:
Japan's invasion of China in 1937 and Germany's attack on Poland in 1939 led directly to the beginning of World War II.
Explanation:
The war causes of the outbreak of World War II were, in the West, the invasion of Poland by the German troops in 1939 and, in the East, the Japanese invasion of China in 1937.
World War II broke out after these aggressive actions received in response a declaration of war, armed resistance or both, by the countries attacked and those with whom they maintained treaties. At first, the allied countries were formed only by Poland, the United Kingdom and France, while the Axis forces were constituted solely by Germany and Italy in an alliance called the Steel Pact.
As the war progressed, the countries that were entering it (due to being attacked or having treaties with the aggressed countries) aligned themselves in one of the two sides, depending on each situation. That was the case of the United States and the USSR, attacked respectively by Japan and Germany. Some countries, such as Hungary or Italy, changed their alliances in the final phases of the war.
