Preventive war

Perhaps the most famous example of preventive war is the attack on Pearl Harbor by the Empire of Japan on December 7, 1941.[14] Many in the US and Japan believed war to be inevitable. Coupled to the crippling US economic embargo that was rapidly degrading the Japanese military capability, that led the Japanese leadership to believe it was better to have the war as soon as possible.[14]

The sneak attack was partly motivated by a desire to destroy the US Pacific Fleet to allow Japan to advance with reduced opposition from the US when it secured Japanese oil supplies by fighting against the British Empire and the Dutch Empire for control over the rich East Indian (Dutch East Indies, Malay Peninsula) oil-fields.[15] In 1940, American policies and tension toward Japanese military actions and Japanese expansionism in the Far East increased. For example, in May 1940, the base of the US Pacific Fleet that was stationed on the West Coast was forwarded to an "advanced" position at Pearl Harbor in Honolulu, Hawaii.

The move was opposed by some US Navy officials, including their commander, Admiral James Otto Richardson, who was relieved by Roosevelt. Even so, the Far East Fleet was not significantly reinforced. Another ineffective plan to reinforce the Pacific was a rather late relocation of fighter planes to bases located on the Pacific islands like Wake Island, Guam, and the Philippines. For a long time, Japanese leaders, especially leaders of the Imperial Japanese Navy, had known that the large US military strength and production capacity posed a long-term threat to Japan's imperialist desires, especially if hostilities broke out in the Pacific. War games on both sides had long reflected those expectations.

The 2003 invasion of Iraq was framed primarily as a preemptive war by the George W. Bush administration,[16] although President Bush also argued it was supported by Security Council Resolutions: "Under Resolutions 678 and 687--both still in effect--the United States and our allies are authorized to use force in ridding Iraq of weapons of mass destruction."[17] At the time, the US public and its allies were led to believe that Ba'athist Iraq might have restarted its nuclear weapons program or been "cheating" on its obligations to dispose of its large stockpile of chemical weapons dating from the Iran–Iraq War. Supporters of the war have argued it to be justified, as Iraq both harbored Islamic terrorist groups sharing a common hatred of Western countries and was suspected to be developing weapons of mass destruction (WMD). Iraq's history of noncompliance of international security matters and its history of both developing and using such weapons were factors in the public perception of Iraq's having weapons of mass destruction.

In support of an attack on Iraq, US President George W. Bush stated in an address to the UN General Assembly on September 12, 2002 that the Iraqi "regime is a grave and gathering danger."[18] However, despite extensive searches during the several years of occupation, the suspected weapons of mass destruction or weapons program infrastructure alleged by the Bush administration were not found to be functional or even known to most Iraqi leaders.[19] Coalition forces instead found dispersed and sometimes-buried and partially dismantled stockpiles of abandoned and functionally expired chemical weapons. Some of the caches had been dangerously stored and were leaking, and many were then disposed of hastily and in secret, leading to secondary exposure from improper handling. Allegations of mismanagement and information suppression followed.[20][21]