Which argument would a historian make as to why the United States was motivated to intervene in the Korean War?

The U.S. wanted to encourage communism from the Soviet Union to Korea.
The U.S. wanted to stop the spread of communism from the Soviet Union to Korea.
The U.S. wanted to ensure the Soviet Union had the necessary support in Greece and Turkey.
The U.S. wanted to better understand the Soviet Union’s military abilities related to the atomic bomb.

The U.S. wanted to stop the spread of communism from the Soviet Union to Korea.