Yeah, that can be possible, though it'd be illegal for a monster to have intercourse with a human or vice versa, so if anyone found out you'd most likely be hunted. @LittleGeekMorgan
War. Since the beginning of time, war has plagued worlds with everlasting death and greed. War is usually started to claim lands from other countries or kingdoms, resources such as food and water or the corruption of gold, diamonds, oil and other things that could sell for a bit of quick cash...