The war is over. But a tone of solemnity reigns over Sri Lanka. Many civilians died, and the country remains highly divided.
But there are things to be learned, even right away. Much of this is speculation, but I think it's good speculation.
I believe the Tigers gave up long after they should have, if military was the only factor. In the past few years, the Sri Lankan military became more competent, and the Tigers failed to revert to an effective insurgency--they fought the Sri Lankan military face-to-face, and lost handily. Cornered for months in a tiny, destitute section of the country, starving and out of ammunition, they held on. They dragged the war on. People continued to die.
I believe the blame lies in part with the international community. The United Nations, the EU, and even the US levered increasing pressure upon the Sri Lankans to pay more attention to civilians, to be more cautious. And the Tigers took advantage of this--one of the reasons so many civilians died was that the Tigers hid among them, and the Sri Lankan government had the domestic political capital necessary to largely ignore this. But increasing international pressure over these civilians may have convinced the Tigers that the tactic would eventually force the Sri Lankans to break and fight much more conservatively.
Moreover, the international community began to advocate strongly for a ceasefire, rather than a surrender. And ceasefires seem to be the knee-jerk reaction of the UN and EU (at least--the US is often responsible). It is a fair knee-jerk; we want the fighting to stop, the dying to stop, as we "sort things out." But the Tamils and the Sri Lankan government had had many ceasefires--and often, they are (quoth a great professor of mine, Barry Posen) "the pause that refreshes" for the losing side. If you are getting beat up badly by your adversary, there's nothing you want more than a ceasefire in order to rearm, reorganize, treat your wounded, recruit, etc. The momentum of the winning side falls apart. Both sides move back--which often means the winning side gives up strategic gains. Sometimes, UN peacekeepers show up to make sure that the winning side can't effectively police the losing side and make sure they don't build up. Such a ceasefire was clearly the last hope of the Tigers, and the incessant calls for it by the international community likely bolstered their confidence in a situation where they would have otherwise felt doomed.
Sometimes, wars must end in surrender. In fact, they often must. Ceasefires lead to lasting peace in very few of the circumstances they are implemented. War does not happen for fun, or out of irrational whim--war is a product of rational security concerns, over competition for naturally scarce security resources that often cannot be allocated well for both sides. The Tigers wanted a homeland to protect themselves as a minority; they were willing to fight, bleed, die, kill, and terrorize for it, for a quarter-century. A ceasefire would not have convinced them to lay down their guns and join the Sri Lankans--not without what is called a "hurting stalemate" (in which both sides have suffered enough and have seen few enough prospects for progress in fighting that a compromise eventually becomes compelling), but a UN-imposed ceasefire typically comes long before that.
The lesson in Sri Lanka is that war sucks, but it cannot be ended by pieces of paper and prayer alone. There are real structural factors at work, and sometimes the best way to change those structural factors to the point that the war ends is to let it run. By pressuring the Sri Lankan government with such zeal, the international community prolonged the war, leading to the unnecessary deaths of hundreds of Sri Lankans. We must not let misguided altruism become an ally of the scourge of war. We must be more conscientious in our statements, in our pressure, in our policy. We must, always, think.