A more thorough explanation:

The separate sovereigns doctrine is a legal principle that allows a person to be prosecuted for the same crime by different government entities without violating the double jeopardy clause of the Fifth Amendment of the United States Constitution.

For example, if a person commits a crime that violates both state and federal laws, they can be prosecuted by both the state and federal government. Similarly, if a person commits a crime in one state and then flees to another state, they can be prosecuted by both states for the same crime.

This doctrine has been controversial because it allows for multiple prosecutions for the same crime, which some argue is a violation of a person's constitutional rights. However, the Supreme Court has upheld the separate sovereigns doctrine as constitutional.