Putting the question that way is maybe a way of helping us think out of the rut - instead of thinking how to stop the war from starting, the attention changes to thinking how to stop it continuing.

Either way it's Stop the War.

And even the ones who want to start it - or to be fair in most cases, see it as necessary to start it (nobody wants to start it, apart from those who have reeason to themselves as the likely beneficiaries, notably Al Qaida, and some parts of the US economy) - even they must see the objective from now on has to be finding a way to end it.