What did Albert Einstein warn the U. S.

about?

He signed a letter addressed to President Franklin Delano Roosevelt, warning that the Nazis might be developing nuclear weapons. Einstein urged the United States to stockpile uranium ore and begin work on its own atomic weapons.

that the Nazis might be making nuclear weapons

Explanation:

In 1939, he signed a letter addressed to President Franklin Delano Roosevelt, warning that the Nazis might be developing nuclear weapons. Einstein urged the United States to stockpile uranium ore and begin work on its own atomic weapons.