Forget U.N. resolutions! After decades of Gaddafi's deadly attacks and his support for terrorist groups across the world, America has every right to seek revenge, says Andrew Roberts.

In all the discussion of where, if anywhere, American strategic interests lie in regard to Libya, one very obvious motivation for U.S. action seems to be being ignored: Vengeance. Yet the certain knowledge that the West will eventually take revenge for terrorist crimes committed even as long ago as the 1970s and 1980s is itself a vital strategic interest. Rogue states must always know that there is no such thing as a statute of limitations on murder, and that even after four decades, the slate has not been wiped clean. The demand for vengeance is not a high-sounding principle of the kind that President Obama might like to intone in his recent speech to the nation, but it has always been an invaluable weapon in the realm of international relations, and its visceral righteousness demands far more respect than windy resolutions of the U.N. Security Council.

On April 5, 1986, a bomb was let off under a table in the La Belle discotheque in West Berlin. It killed a Turkish woman and two American sergeants and injured 229 people, including over 70 U.S. servicemen, some of whom were maimed for life. The outrage was authoritatively traced back to Colonel Gaddafi, only three months after the United States had imposed sanctions on Libya for his links to international terrorism. Five days after the disco bombing, planes from U.S. warships and bases in Britain—France having refused them permission to fly over its airspace—bombed various targets in Libya, killing over 100 people, including Colonel Gaddafi's infant daughter.

Before the attack, Gaddafi had broken off relations with Saudi Arabia because of what he called the "U.S. occupation" there. He had bought huge amounts of arms from the USSR, and his MIG jets "played chicken" with American planes near the Libyan coast. When oil was discovered between Libya and Malta, he declared that the territorial waters of Libya included everything up to 12 miles from the Maltese shore. He invaded Chad and sent death squads into Nigeria. As an account of these events recalls, Gaddafi "had an affection for resistance fighters and revolutionaries everywhere, no matter whose side they were on. To give you some idea, he funneled money and arms to Scottish revolutionaries."

Western vengeance might take time, but it will eventually be served.

The list of "national liberation" movements that Gadaffi supported financially or with arms represented a virtual encyclopedia of extremist groups, and has included the Moros in the Philippines, the Palestine Liberation Organization, the New Jewel movement in Grenada, the IRA, the Basques, the Kurds, Louis Farrakhan's Nation of Islam, and the Black Panthers, as well as guerrilla movements in Chad, Eritrea, Lebanon, the Canary Islands, Egypt, Sudan, Corsica and Sardinia and even Wales. The havoc that these groups have caused in the West and elsewhere cries out for vengeance.

Nor should we neglect Gaddafi's most outrageous crime against America and the West. On December 21, 1988, Pan-Am Flight 103 was destroyed by a bomb over Lockerbie, killing 243 mainly American and British passengers, 16 crew and 11 people in the town below. In February this year, the former Libyan justice minister Mustafa Abdel-Jalil confirmed what everyone has always known all along: that Gaddafi personally ordered the attack. If revenge is indeed a dish best served cold, then now, 23 years later, that dish is near-freezing, and will taste all the better.

Try as the Obama administration might to justify the no-fly zone and Tomahawk attacks by reference to stabilizing Tunisia and Egypt, or preventing The Rape of Benghazi, or stopping a refugee crisis on the Mediterranean, the real reason why NATO should now take active steps to topple Gaddafi is to avenge the cold-blooded murder of American servicemen and civilians in terrorist attacks during the 1980s. It will send a lesson to other states: Western vengeance might take time, but it will eventually be served.

Historian Andrew Roberts' latest book, Masters and Commanders , was published in the UK in September. His previous books include Napoleon and Wellington, Hitler and Churchill, and A History of the English-Speaking Peoples Since 1900 . Roberts is a fellow of the Royal Society of Literature.