Answer:
The main reason why <em>Einstein</em> urged <em>the president</em> to authorize the project known as the “Manhattan Project” is because <em>Germany</em> was also developing <em>atomic bombs</em>
Explanation:
Back in <em>1939</em>, the president of the US was Franklin D. Roosevelt. In this period <em>Einstein</em> and other scientists were close to developing an atomic bomb.
Becuse that Germany was also close to figuring out how to make an atomic bomb, a scientist and the co-worker of <em>Einstein</em>, <em>Szilard</em> wrote a letter to the president urging him to authorize the Manhattan project. This letter was just signed by <em>Einstein (not written)</em>.
The decision was made and the project was active.
Still, the important fact is that <em>Einstein</em> himself was not later included in the project. At that time, he was considered a kind of celebrity and his own safety would have been in jeopardy if he had worked on it. The project’s info was basically denied to <em>Einstein</em> and the only contribution from his side was several equations.
At the end of the project, when the atomic bombs were already created and the decisions of their dropping points made, <em>Einstein</em> found out everything about the project and as <em>he</em> said, <em>he</em> regretted signing the letter.