Jurisdiction requirement: The court must have SMJ, which can be based on federal question or diversity.

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Subject-matter jurisdiction determines whether a federal court has the power to hear a case. It can be based on a federal question (a claim arising under federal law) or on complete diversity of the parties with the amount in controversy meeting the statutory threshold. When a party wants to join additional claims or parties, the court still must have SMJ over the action as a whole. That means the presence of joinder doesn’t create SMJ out of nothing; the overall case must be within federal jurisdiction, secured either by a federal-question basis or by diversity. The other options misstate the requirement: SMJ isn’t optional for joinder, personal jurisdiction (PJ) does not provide SMJ, and relying solely on state-court jurisdiction doesn’t justify federal jurisdiction for a federal-question or diversity-based claim.