If (All Conditions are True) then do (Then Actions) else do (Else Actions)
If - Conditions
(Number of living Town Hall units owned by Player 1 (Red)) Equal to 0
Then - Actions
Game - Defeat Player 1 (Red) with the message: Defeat!
Else - Actions
However, there are a few problems that may arise with that Although this should give you a general idea (Heck, I don't even know if this trigger will work).
I'm on a page about incorrect corrections, and spent the better part of like two hours trying to get someone to understand that -5^2 = -25, not 25, and then that post had comments get reposted because that group is self sustaining, and that person was in turn trying to explain what I just explained to them. And I'm taking that as a victory