What caused the western territories to join the American Revolution?

the American revolution only included the 13 colonies (Britain's colonies in what is now America). the western territories of America had nothing to do with it. the western side of America only joined the US when US president James K. Polk came to power and introduced the idea of Manifest Destiny, which is the idea that Americans are entitled to own all of North America. :) the territories had no choice of joining America or not.