Why did palmer arrest thousands of people and deport hundred between 1919-1920?

These were called the Palmer raids and were a part of the red scare. He did it because they were accused of being communists and anarchists, or were just too much left and liberal. This was out of fear that they might get enough people and start their own revolution in the country.

The Palmer Raids occurred between 1919 and 1920 under the leadership of General Palmer. These were an effort by the United States Department of Justice to identify and deport radical leftists and extremists. More than 500 citizens were arrested and deported during this time. This was a part of the Red Scare, which was a fear of communist radicals that occurred after World War One.