Minimal Diversity is different from Complete Diversity
Minimal diversity means that at least one plaintiff is a citizen of a different state from at least one defendant. As a general rule, for purposes of diversity subject matter jurisdiction, that is insufficient. A federal court can only assert diversity subject matter jurisdiction if there is complete diversity, meaning no plaintiff can be a citizen of the same state as any defendant.
In the picture to the right, we lack complete diversity because there is a plaintiff and a defendant from New York. There is only minimal diversity, which in most cases will not confer diversity jurisdiction on a federal court.
There are a few exceptions created by statutes:
28 USC 1335: Interpleader
28 USC § 1335 is the federal interpleader statute. In an interpleader action a plaintiff sues defendants who both claim the right to property or money in plaintiff’s possession to enable the court to determine to whom plaintiff should provide the property or money. The interpleader statute only requires minimal diversity. You can read more about interpleader here.
28 USC 1332(d): Class Actions
28 USC § 1332(d) is one section of the Class Action Fairness Act of 2005 (CAFA). CAFA empowers federal courts to assert subject matter jurisdiction over class actions in which the amount in controversy is greater than $5 million, there are at least 100 plaintiffs in the class, and there is minimal diversity. Complete diversity is not required in these types of class actions.
28 USC 1369: Multiparty Multiforum Jurisdiction
Under 28 USC § 1369, minimal diversity will be sufficient for diversity jurisdiction where an incident kills at least 75 people and certain other factors are met.