Article I, Section 10, clause 3 of the U.S. Constitution requires that "No State shall, without the Consent of Congress, ... enter into any ... Compact with another State ...."
There were only 36 interstate compacts in nearly 140 years, spanning from 1783 to 1920, states, and most of them were established merely to resolve boundary disputes. Since 1920, and particularly since World War II, there have been more than 150 new interstate compacts, and today the average state belongs to about 25 such compacts.
- US Government and Politics