When Canadian CF-18 warplanes dropped hundreds of laser-guided bombs on Libyan targets in 2011, the devastating strikes were lawful – backed by an explicit authorization of force from the United Nations Security Council. Still, some claim that the NATO-run air war, commanded by a Canadian air force general, grossly over-reached the UN mandate to protect Libyan civilians and instead operated like the rebels' air force until Moammar Gadhafi was toppled.
When Canadian CF-18s dropped hundreds of laser-guided bombs on Serb targets in 1999, the attacks lacked UN legitimacy because Russia and China – both veto-wielding powers at the Security Council – were staunchly opposed. NATO powers attacked Serb forces anyway, claiming they had a moral and legal obligation to protect Kosovo's Albanian majority, threatened with mass expulsion and genocide.
Ever since 1945, Canadians have marched into battle and flown combat missions within, on the margins of, and, sometimes, beyond the boundaries of legitimate war as now governed by the UN Security Council. In the 1950s war in Korea, the 1991 Gulf war to oust Iraq from Kuwait and the still-unfinished conflict in Afghanistan, the Security Council approved clear mandates authorizing the use of military force.
But the absence of UN legitimacy, however desirable as political cover, hasn't stopped the Western allies from launching military attacks when they have wanted to, a lesson that may be repeated in Syria.
Russia tried, but failed, to have the Kosovo air war branded as unlawful, putting forth a Security Council resolution that said "such unilateral use of force constitutes a flagrant violation of the United Nations Charter." The resolution failed and the bombing continued.
Kosovo may serve as the likely template for any U.S.-led attacks on Syria, given Russia's avowed determination to veto any resolution that would give it legitimacy on it and President Barack Obama's apparent willingness to take military action with or without a UN mandate.
UN-mandated military missions fall into two broad categories, known by the chapters of the UN Charter.
Chapter Seven operations are authorized wars that range in scale, scope and duration. Usually, the UN delegates the conduct of the action to a coalition of nations. In most of the high-profile instances, that coalition is often led by the United States. The massive 100-day air war, followed by the huge U.S.-led armoured onslaught to drive Iraq from occupied Kuwait in 1991 by a coalition of dozens on nations, is perhaps the most clear-cut example of a UN-mandated and widely accepted response by the international community. But Chapter Seven can be invoked in small wars too, such as the joint U.S.-Canada operation in Haiti in 1994 to force the removal of President Jean-Bertrand Aristide. Others, like Somalia in the 1990s, fail despite plenty of firepower.
Chapter Six operations are usually dubbed "peacekeeping", although sometimes there is no peace to keep. Still, the force authorized is far more constrained. Usually UN-mandated troops on Chapter Six operations can only open fire in self-defence or to protect those working for the UN. Some peacekeeping operations can be large and militarily robust – like the tens of thousands of 'blue helmets' deployed in Bosnia during the violent breakup of Yugoslavia in the 1990s. But those troops, including Canadians, had no mandate to defend even UN-designated safe havens like Srebrenica. Other Chapter Six missions may involve nothing more than lightly-armed military observers. One key distinction is that Chapter Six missions operate with the permission of the state involved – which can also toss them out – and can range from full-blown expeditionary forces just short of war to humanitarian relief with militaries providing logistics and support.