Einstein primarily emigrated to the United States because he had a Jewish background, and Adolf Hitler, who became Germany's chancellor in 1932, was about to adopt Anti-Semitic policies.
It was a very hard choice for Einstein to choose to emigrate to the United States, but it was a very wise one. As a Jew, he knew what was gonna happen if he stayed in the United States. You may already know that the Holocaust happened a few years later, in which most Jews living in countries occupied by Germany were murdered. Thanks to moving to the U.S, Einstein was safe from this event.
