The United States legal system is an adversarial system. Civil suits cannot be initiated by third parties, but must be filed by the aggrieved party who seeks redress. Generally, the action is initiated in the jurisdiction where the event occurred, where the defendant can be served or where the parties have agreed to have the case located. The filing of a complaint or "prayer for relief" is a voluntary action by the person aggrieved, and as a necessity of this request, the person seeking relief consents to be bound by the judgment of the court. The doctrine of consent is also extended to defendants who attend and litigate actions without challenging the court's personal jurisdiction. Consent may also derive from a pre-litigation agreement by the parties, such as a forum selection clause in a contract (not to be confused with a choice of law clause). Doctrines such as claim preclusion prevent re-litigation of failed complaints in alternative forums. Claim preclusion does not, however, prevent the refiling of a claim that was filed in a court that did not have personal jurisdiction over the defendant.