The US never wanted to join World War II so they isolated themselves from everything that was going on and tried to stay neutral (Over time, we sided with the Allies). Mainly, we entered due to the Japanese attack on Pearl Harbor. After the bombing, the US decided to declare war on Japan. Soon after, Nazi Germany's leader declared war on the US and then the US was officially in the war.
So, all in all, it was the bombing of Pearl Harbor on December 7, 1941.
Hope this helps :)
The Gupta Empire was an ancient Indianempire, founded by Sri Gupta, which existed at its zenith from approximately 320 to 550 CE and covered much of the Indian subcontinent. The peace and prosperity created under the leadership of the Guptas enabled the pursuit of scientific and artistic endeavours.This period is called the Golden Age of India and was marked by extensive
