I don't know how to explain my question but basically I don't follow politics much and for instance can't really tell the difference between liberal/conservative vs Democratic/Republican, but recently someone asked me about my views and they were surprised because apparently I like some things from Democratic party and some from Republican (or from both conservatives and liberals). I started to wonder if I am an anomaly because apparently most people belong to one of the two parties (and rarely to green party).

Just to give a concrete example, for instance I don't understand why belief in strong national defense has to go hand in hand with being anti abortion and anti gay marriage. Yet those views do go together, in Republican party. Or why does religion and being in favor of free enterprise go hand in hand? Or to pick another example, this time from the democratic party, why is being pro gay marriage also means being pro abortion, and protecting the environment.

I don't know if my question has more to do with history of US and its culture and society (perhaps in some other country or at some other time in future it's atheists who are pro free enterprise and the religious being against), or with human psychology? Or maybe it's one of those questions that has no answer, and it is the way it just because.

I figured I ask here and maybe someone can explain it to me or direct me to some readings.