In a case where a plaintiff from State A sues a defendant from State B, what is an essential element for establishing diversity jurisdiction?

To establish diversity jurisdiction under U.S. law, one of the crucial elements required is that the parties involved are citizens of different states. This fundamental principle ensures that federal courts can hear cases involving parties from different jurisdictions, which aims to prevent local bias in state courts. By requiring that the plaintiff and defendant are from different states, the legal system promotes fairness in adjudicating disputes that cross state lines.

While other factors, such as the amount in controversy and the nature of the claim, are important in determining jurisdiction and whether the case can proceed in a federal court, the core requirement is the diversity of citizenship. Specifically, under 28 U.S.C. § 1332, a case can only qualify for diversity jurisdiction if there is complete diversity, meaning no plaintiff can be a citizen of the same state as any defendant. This ensures that the interests of both parties are represented equally in a federal forum, presumably free from potential bias that could arise from a state court sympathetic to its own citizens.

In summary, the requirement of having parties who are citizens of different states is essential for establishing diversity jurisdiction, making it the correct answer in this scenario.