During the Japanese expansion of 1931-41 and the attack on the American base Pearl Habor, 7 December 1941.

Use the dates listed:
1. Before 1918
2. 1931-1933
3. By 1938
4. 1938-1941
To write a sentence about each time period listed above

1. Before 1918: Japan was primarily focusing on internal development and modernization, aiming to catch up with Western powers through various social and political reforms.

2. 1931-1933: Japan's expansion kicked off with the invasion of Manchuria in 1931, followed by the establishment of the puppet state of Manchukuo and the withdrawal from the League of Nations in 1933.

3. By 1938: Japan had successfully occupied a significant portion of northern and coastal China, including major cities such as Shanghai and Nanjing, leading to the infamous Nanjing Massacre.

4. 1938-1941: Japan continued its military aggression in East Asia, with further invasions of China, including the capture of the capital city, Beijing, in 1937. The period also saw the signing of the Tripartite Pact between Japan, Germany, and Italy in 1940, solidifying their alliance. The attack on Pearl Harbor on December 7, 1941, marked a turning point, as Japan directly challenged the United States and launched its Pacific conquests.

In simpler sentences

1. Before 1918: Japan was focused on modernizing and catching up with the Western powers through social and political reforms.

2. 1931-1933: Japan started expanding by invading Manchuria and creating a puppet state called Manchukuo.
3. By 1938: Japan had taken control of parts of China, including major cities like Shanghai and Nanjing, leading to the Nanjing Massacre.
4. 1938-1941: Japan continued its military aggression in East Asia, invading more of China and forming an alliance with Germany and Italy. The attack on Pearl Harbor in 1941 marked a major turning point.

Answer the fourth time period with one simple sentence

From 1938 to 1941, Japan continued its military aggression in East Asia, leading up to the attack on Pearl Harbor in 1941.