Which event prompted the investigation that led to these findings? The Cuban Missile Crisis
The Iran hostage crisis
The bombing of Pearl Harbor
The September 11 terrorist
attacks

It’s September 11 terrorist attacks

Explanation:

Because if you scan the bottom of the letter with the name it comes up in the web

australian plates collided into eurasian plates, and the himalayas formed. the andes mountain range the himalayas and the islands of japan form differently. the andes mountain range formed at the convergent boundary of an oceanic plate and continental plate.

they gained control over the philippines, east dutch indies/indonesia, much of new guinea, the solomon islands, guam, and other strategic areas all over the western pacific. japan even occupied part of the aleutian islands, which belonged to alaska.

source:

have a great day