The Tri-Nation Alliance didn't drag the time to the last minute of the seventy-two hours. They formally submitted their letter of surrender through the ambassador stationed in the Victor Empire before dark.
Even though the Tri-Nation Alliance thought about struggling a bit more, their capital was utterly destroyed, with millions dead or injured domestically, and another million displaced and in urgent need of aid, which hit them so hard that they couldn't organize any effective resistance.
Not to mention, the entire national government institutions were wiped out, making it hard to find someone temporarily to take the blame and sign the surrender.
Fortunately, only their capital was wiped out, leaving other important cities intact. After some time spent squabbling, they still managed to elect an interim government leader who then came forward to announce the surrender.
There was no way but to surrender, as no one dared to defy Victor Empire's war threats.
