ELI5: Explain Like I'm 5

Tenth Amendment to the United States Constitution

The tenth amendment to the United States Constitution is often called the states' rights amendment. It says that the federal government (the government of the United States of America) can only do the things it's allowed to do by the Constitution. Anything else is up to the state governments. The amendment is like a promise that the federal government won't try to take away any of the powers of the states.