Except that this is very rarely the case, including with Attila. Most civs hit their neighbours first, and I quite often go entire games as the one neutral party amid AI civs at war with one another (also, for some reason, certain civs love to attack city-states - in every recent game he's been in Nebuchadnezzar has declared very early war against a neighbouring CS without provocation, presumably to bowman-rush a city he can capture).