The standard criteria in international law, developed by Daniel Webster, for an "imminent threat", is when the need for action is "instant, overwhelming, and leaving no choice of means, and no moment for deliberation." In such a case, he argued, the use of force in self-defense is justified. Source: Wikipedia.
- Daniel Webster, "The Papers of Daniel Webster": Diplomatic Papers 67, 1983. [Footnote #3: "In 1837, the British attacked and destroyed the U.S. ship Caroline, which the British had suspected of being used by Canadian insurgents along the Canadian-American border. The ship was moored in an American port, with an American crew. On April 24, 1841, Webster wrote to the British Ambassador to the U.S., Henry Stephen Cox, to protest this action."]
- Neta C. Crawford, "The Best Defense: The problem with Bush's 'pre-emptive' war doctrine," Boston Review, February/March 2003.
- Steven C. Welsh, "Preemptive War and International Law," Center for Defense Information, December 5, 2003.
- Scot J. Zentner, "Friends, Enemies and the War in Iraq: A View from the Founding," NexusJournal.org, July 12, 2004: "In a well-known expression of this principle, Daniel Webster argued that a government that engages in preemption must 'show a necessity of self-defence, instant, overwhelming, leaving no choice of means, and no moment for deliberation.'"
- Cassandra J. Keyes (Cadet), "Defining Just Preemption," JSCOPE Conference 2005, U.S. Military Academy, West Point, NY, January 3, 2005.
- Henry Shue, Prof., "International Normative Theory, Lecture 2: Pre-emption: Defence Before the Attack?," University of Oxford, Department of Politics and International Relations, Merton College, Hilary Term, January 27, 2005.