the only reason a no fly zone would cause war is because russia doesn't want it. thus, enforcing the no fly zone by shooting down russian planes would cause war. however, i have no reason to believe clinton wants the US to take it upon itself to enforce a no fly zone in syria when international organizations have already discussed this and shot down the idea, especially because of objections from countries like russia that don't want one. and this is exclusively why it would cause war as far as i can tell. if clinon got russia to agree to a no fly zone, there would be no war, and with no agreement, there would be no no-fly zone.