Permit me to wade in on both of David's comments and Mark's initial input. Getting the mandate right is like getting the re-entry angle right on Apollo capsules return from the moon: too shallow and they'd skip off into space; too deep and they'd burn up. And they couldn't be steered once re-entry started. Peacemaking and peace accords set the initial "re-entry angle" for peace implementation: too shallow and the polity doesn't recover (Haiti 1994+); too deep and the commitment may burn out (Somalia then, perhaps Afghanistan now). As I tell my students, the international community has the resources for many shallow or a few deep interventions but not both and not in big places. Unlike Apollo, mandates can be steered, but ultimate results may be above their pay grade. Thus, MONUC in DRC evolved from protected observation into a big, violent holding action but its problems will not be solved by whatever the mission might do, even with different nationalities in its troop makeup, because the fundamental problem is higher-grade, in the political leadership decisions of Congo, the surrounding states, and those in Congo who periodically serve as their proxies. The "weight to do right" must be felt in those capitals. Darfur is not even, as yet, a holding action, its fate tied more closely to politics in Khartoum than to whatever peacekeepers might manage to do in the field.

Regarding David's note on the novelty of developed state participation in complex UN ops: it was norm for a few years after the Cold War, with large Western contingents in UNPROFOR (Bosnia -- Britain, France, Spain, the Netherlands, and the Nordics) and UNOSOM II (Somalia -- US, France, Italy, Australia, Belgium). Plus Rwanda (Belgium again). Since then, command and control complaints have been the excuse for non-participation in UN ops but Western hands were all over the control levers in Bosnia, Somalia, and Rwanda. But the issue of whether UN C2 has improved enough in 15 years is mooted by western commitments of troops under other flags (NATO, EU).