A more thorough explanation:

The Compact Clause is a provision in the United States Constitution, specifically in Article I, Section 10, Clause 3. It prohibits states from entering into agreements or contracts with other states or foreign countries without the approval of Congress.

For example, if California wanted to enter into a trade agreement with Mexico, they would need to get approval from Congress before doing so. This is because the Compact Clause is designed to prevent states from making agreements that could potentially harm the interests of the United States as a whole.

Another example is if two states wanted to form a compact to share resources, such as water or electricity. They would need to get approval from Congress before doing so, to ensure that the agreement does not violate any federal laws or harm the interests of other states.

The Compact Clause helps to maintain the balance of power between the federal government and the states, by ensuring that states cannot make agreements that could potentially undermine the authority of the federal government or harm the interests of other states.