Consider the most famous--or infamous--humanitarian intervention of recent years, in Somalia in the early 1990s. The mission went down in history as a disaster, but there were actually two phases to the operation, and they enjoyed very different degrees of success.
The first phase, from December 1992 to May 1993, was a U.S.-dominated venture called UNITAF, with 28,000 American troops. This well-organized intervention was highly successful at stabilizing southern Somalia and facilitating the delivery of aid, and may have saved 100,000 Somali lives. So far so good.
But in May 1993, UNITAF handed over to a UN operation called UNOSOM II, with a much-diminished U.S. role. UNOSOM II's motley collection of troops from Botswana, Bangladesh, Pakistan, Italy and elsewhere, were no match for U.S. forces, and arrived without even basic equipment. Worse than that, no single country provided leadership. Instead, each member of the coalition pursued its own agenda. The United States, for example, pushed for an aggressive strategy to isolate the Somali warlord General Aideed. Meanwhile, Italy favored a conciliatory approach, and declined to follow the orders of UN commanders. The mission eventually unraveled in the wake of the October 1993 Black Hawk Down battle in Mogadishu, when eighteen Americans died.
The large number of coalition members in UNOSOM II wasn't a force multiplier. Instead, it was America's ticket to reduce its role and then exit precipitously. The Clinton administration gained political cover for the U.S. withdrawal from Somalia by falsely blaming the United Nations for Black Hawk Down--even though Washington had actually masterminded the mission in Mogadishu.
The intervention in Libya looks more like UNOSOM II than UNITAF, with no clarity about which country is running the show--and too many cooks spoiling the broth. At first glance, the British and French might appear to be co-head chefs, but neither seems to be in control. The Americans have experience of running these operations, but they don't want to own this particular dish.
NATO allies are so weak militarily--relative to the United States--that they bring few real assets to the table. U.S. Defense Secretary Robert Gates said this week: "The mightiest military alliance in history is only 11 weeks into an operation against a poorly armed regime in a sparsely populated country, yet many allies are beginning to run short of munitions, requiring the U.S., once more, to make up the difference."
What the NATO allies do bring to the table are a variety of restrictions over what their military forces will and won't do in Libya. A core group of countries, including the UK, France, the United States and Canada, are carrying out most of the airstrikes. But Spain, the Netherlands and Turkey won't even allow their aircraft to engage in ground attacks. Almost half of NATO isn't contributing any forces at all, including Germany and Poland. There are also divisions over arming the Libyan rebels. Qatar and Italy have supported handing over weapons. Belgium and Denmark are more skeptical.