The Anti-Imperialist League was strongly against countries like the United States, who had a strong military, government, and economy, taking over weaker nations. These weaker nations had no resistance and the stronger countries would show their dominance of cultural superiority and military power over these people.
One example of this with the United States was Hawaii. Hawaii was forcefully taken by the United States as an imperial power, whereas the people of Hawaii had no defense or ways to stop the United States from taking them over.
The Anti-Imperialist League believed these types of actions were wrong and that our country should follow a more isolationist view and stay out of other country's affairs.
