If you look at the different
types of government ideologies throughout the world, past and present, There is,» Communist, Fascist, Theocratic, Democratic, Republican, ect...» Notice how atheism doesn't fit because atheism is not, like you stated is it, a world view, but rather a rejection of religious world views.
So they focus on other aspects
of their
ideology: for example, within the world that relies on markets, they feel like their differences come from something else, such as their
type of government (republic versus monarchy versus whatever) or within the muslim world they focus on their religious families (are we more sunnites or more hiites or etc..)