The other reply is that peaceful relations must necessarily precede the creation of the common institutions. This explanation holds that the richer a state, the more it has to lose in the devastation of war, thus the less likely it is to engage in war. Democracies, at least until the last decade or two, have usually been wealthy, thus between themselves there are double disincentives against conflict. This argument is much like the argument that trade and investment make peace. The problem with both these arguments is that there are plenty of counter examples.
Peace often exists between states with weak economic ties and between poor states.
Also both trade and wealth can generate competitive aggression. The answer sadly has to be no . When other nations are seen as also possessing these political norms they are perceived as legitimate, possessing restraints on governmental excesses and not likely to be out to dominate us. We in turn do not wish to dominate them because their conduct conforms with our professed norms. The perceived legitimacy of the fellow democratic state operates as a powerful restraint on any impulse to overthrow such a government both internally and internationally.