A more thorough explanation:

Diversity of citizenship refers to a situation where the plaintiffs and defendants in a lawsuit are citizens of different states. This means that there is no common state citizenship between the parties involved in the case. When this happens, plaintiffs can bring their claims to federal court instead of state court, and defendants can remove cases from state court to federal court.

The purpose of diversity jurisdiction is to provide an unbiased court for out-of-state litigants. If a plaintiff and defendant are both citizens of the same state, there is no need for diversity jurisdiction because there is no threat of bias based on citizenship.

For example, if a person from California sues a person from New York, and the amount in controversy meets the requirement, the case can be heard in federal court because there is diversity of citizenship. However, if a person from California sues another person from California, the case must be heard in state court because there is no diversity of citizenship.

According to 28 U.S.C § 1332, a corporation is considered a citizen of both the state in which it is incorporated and the state where its principal place of business is located. For example, if a corporation is incorporated in Delaware but has its principal place of business in California, it is considered a citizen of both Delaware and California.

Unincorporated associations, such as partnerships, are considered citizens of each state where at least one of its members is a citizen. For example, if a partnership has two members, one from Texas and one from Louisiana, the partnership is considered a citizen of both Texas and Louisiana.