Which of the five principles of politics best explains why the federal government passed the americans with disabilities act of 1990 to adopt uniform standards across the states rather than leave it to the individual states to determine how to increase access to public buildings for the disabled?

The correct answer is the collective action principle

This principle revolves around the idea that a group of people should work together in ensuring the well-being of everyone. If they had left it to states, numerous states probably wouldn't bother with such things because of various reasons, either financial or lack of care for people with disabilities. Because of the collective action principle, they now had to help everyone.