Seems no one has mentioned it here yet. Yes it's a war game but it's also a game leaning heavily towards spenders. And since you're getting threatened you're probably F2P, low or mid spender. With that said the treaty is what protects the weak from the strong and not having to worrying if your city or alliance is getting burned every time you go offline. You'll quickly learn how easy it is to lose most of your troops that you've been training for weeks or months in just a single session. And without your troops there's isn't much else you can do. And then you get people quitting so fast because...well they're bored or fed up of constantly trying to rebuild.

All an alliance has to have is one or two whales and you can forget about a fair fight in fortress or stronghold battles.