What was the main reason that congress passed the indian removal act?

The main reason was the dispute over the lands of the Native tribes.

Explanation:

The governments of several states of the United States felt that the presence of the tribes was a threat to peace and security, because many Native Americans had fought against the United States in previous wars, often armed by foreign nations such as Great Britain and Spain. Other white settlers and land speculators simply wanted the land that was being occupied by the tribes. Therefore, these governments wanted all tribal lands within their borders to be placed under state jurisdiction.