No Gareth, noone under any circumstances has the right to take innocent people hostages and threaten to kill them, even if their demands are totally just. But even if they do so, that doesn't make the thing they are demanding any less a just demand.

That's why I gave the extreme imaginary example I did, about Jews in face of the Holocaust.

Waging an unjust war in effect means taking a whole country hostage. In fact it means taking at least two countries hostage, since the people of the home country are also held hostage, more esopecially the conscripts in the army.