An ultimatum () is a demand whose fulfilment is requested in a specified period of time and which is backed up by a threat to be followed through in case of noncompliance. An ultimatum is generally the final demand in a series of requests. As such, the time allotted is usually short, and the request is understood not to be open to further negotiation.

The threat which backs up the ultimatum can vary depending on the demand in question and on the other circumstances. The following are commonly encountered:

• in diplomacy, the threat to declare war, to take other military action or to impose sanctions such as trade restrictions or embargoes.
• in a kidnapping, the threat by the kidnappers to kill the hostages, or by the authorities to seize them back by force.

In everyday life, ultimatums are also sometimes made in various contexts, such as in:

• a legal proceeding (e.g. the demand to strike a plea bargain or face a trial)
• a business relationship (e.g. the demand to accept a certain price or to forgo the deal)
• a personal relationship (e.g. the demand to desist in an extramarital affair or to face a divorce).

Such ultimatums may or may not be legal and/or socially acceptable. Ultimatums are also a regular part of the crime of extortion.

See also

• Ultimatum game

Laws of war

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