The idea that there are good and evil (or lawful and chaotic) gods constantly struggling against each other is ubiquitous in fantasy fiction, but it's not particularly common in world mythology. Usually the epic battles between gods took place in the distant past or will take place in the future. In the present, the gods are constantly working in the world - making sure the rain falls, and people are born and die, and plants grow, etc. - but they're not typically in conflict with one another.
Well, yes and no. Many ancient people saw the conflicts on Earth reflected in the heavens. If you were at war with the neighboring city, that meant your god was also at war with their god. If you won, that meant your god also vanquished their god. If you lost, then your god was also defeated. Often times, conquered peoples would adopt the deities of their conquerors having realized that their old god wasn't up to snuff.