Damn, Sentries and princesses can be very oppressive... and theres no mining your way to victory either. Id imagine a game going that long, everybody has a ton of specialists and their counter.
I think this situation is pretty rare, so I don't know if it warrants a specific button to stop it. In my general experience, dominion has been pretty fast pace, with one or two snowballing out of control.
Back to your situation, as it is oppressive and sounds very slow. Perhaps you could arrange for a Sentry Ceasefire, by either evacuating your princesses from the sentries or having your sentries take a stroll in a sub.
Because there are a lot of princesses I'd imagine everybody can see what everybody is doing. If some guy doesn't remove a sentry or princess, perhaps dog pile on em?
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