Umm... The roman empire didn't have roving submarines with thermonuclear ability. If somone were to pull shit, it doesn't matter which country started it, cause they will end up as a pile of rubble.

That's why we have nothing to fear from any sane country (Russia, China, etc), just religious zealots, terrorists, and rouge states like NK. And those countries would be hard pressed to pull an upsurp like that.