Who won the Mahabharata war?

Militarily the answer is simple. By the evening of the eighteenth day every Kaurava brother is dead, Duryodhana lies broken by the lake at Samantapanchaka, and Yudhishthira is crowned king of Hastinapur with the blind Dhritarashtra still honoured in the palace.

The epic refuses to let that stand as a victory. On the night after the last day, Ashwatthama enters the sleeping Pandava camp with Kripa and Kritavarma and kills Dhrishtadyumna, Shikhandi and the five young sons of Draupadi in their beds. The Pandavas survive only because they were not in the camp. Their heir Abhimanyu died on the thirteenth day, Ghatotkacha on the fourteenth night, Drupada and Virata earlier. Of eighteen armies almost no one is left. Yudhishthira reaction is not triumph but a refusal to be crowned, and the whole of the Shanti Parva is Bhishma trying to talk him out of abdicating.

The reckoning continues after the war. Gandhari, who has lost a hundred sons, curses Krishna to watch his own people destroy each other and to die alone; thirty-six years later that happens. The Pandavas rule, install Abhimanyu posthumous son Parikshit, and then walk into the Himalaya to die. Only Yudhishthira reaches the end of that road alive.

The word the epic chooses matters. Its refrain is that where dharma is, there is victory, yato dharmas tato jayah. It never says that victory proves dharma was there.

There is a second, quieter reckoning in the final books. Yudhishthira is shown Duryodhana seated in heaven, honoured for having died facing his enemies as a kshatriya should, while his own brothers appear to be elsewhere. The epic will not let the winners hold even the afterlife uncontested.