What concept did American colonists believed justified their demand for a new government?

The concept of "no taxation without representation" was a key belief that justified the American colonists' demand for a new government. They believed that as they were being taxed by the British government without having any representatives in Parliament to speak on their behalf, they were being denied a basic right of self-governance. This belief fueled the American Revolution and ultimately led to the creation of the United States as an independent nation.