Only one body can provide the leadership that's needed to defeat the insurgencies in both Iraq and – over a longer time frame – Afghanistan. That is the United Nations. Though it's far from a perfect institution, only the UN has the vital quality of worldwide legitimacy that allows it to mobilize global resources and expertise and make the tough decisions required in these two countries.
Regarding Iraq, we need to ask the UN to urgently convene two negotiating forums. One would sort out the thorny political dilemmas that remain inside the country. The other would bring together Iraq, all its neighbors, the US, and perhaps also the Arab League to agree on a plan for the drawdown – or total withdrawal – of US forces in a way that will not result in Iraq's neighbors moving in to exploit the resulting vacuum.
Americans have a similar need for a greatly increased UN leadership in Afghanistan. Given the current state of world politics, it is quite improbable that the US and its NATO allies can ever achieve the "pacification" of a country so far distant from NATO in geography, culture, and politics.
Former national security adviser Zbigniew Brzezinski is just one of those now warning the US against being drawn into the same trap that confounded the Soviets in Afghanistan. Other non-NATO governments need to be brought into the decisionmaking. (The stakes that many of them have in preventing the Afghan state from failing yet again are just as high, or higher than, our own.)