Empires At War Victory

In my new map "Empires At War" I have it so if a City Hall's hit points are reduced below 30% then that person allies the attacker, shares vision and changes to the color of that person. I'm wondering what would be the best way to have a victory trigger for whoever conquers everyone.

The notion of who conquers everyone is illdefined. You'll have to think of a rigorous definition of victory then come back to T&S if you need help implementing it.
This is somewhat similar to voting in the difficulty of defining victory and the opportunities for collusion, so I would use similar solution techniques. First define criteria that your victory algorithm should satisfy. For example, if one person is never conquered, that person should be the victor. Then try to invent an algorithm that satisfies as many criteria as you can manage. Like voting it will probably be impossible to satisfy all of them.

Moved to gen dev

I made a similar map based on warcraft units, your welcome to look over the code.