Question

Can somebody help me restate my thesis so that it sounds more developed. So my thesis is “Dropping th atomic bomb on Japan was necessary because the U.S. provided them with multiple warnings and it enabled the war in the Pacific to come to a swift end.” I want to rephrase that to make it sound more sophisticated any ideas on how I should phrase it ?

Answer 1

Oh boy. Here's my attempt at it: The atomic bomb drop in Japan was necessary because the Japanese were warned multiple times by the U.S. about it, and it enabled a swift end to the war in the Pacific. Hope this helps!

Answer 2

Using the atomic bomb on the Japanese in WW2 brought the war in the Pacific to an abrupt end. Even after they experienced the devastation of Hiroshima, there was no word from the military leaders that they were ready to surrender. Three days later, the Americans added Nagasaki to the two cities that were destroyed by a single weapon. That brought the immediate surrender of Japan. These two facts will be used to show .... 

that the world had been brought into a new era of warfare.  Perhaps.

There is no reason why you need just one sentence as a thesis. And what you wrote, to be truthful, is as good if not better than what I wrote. It's shorter.