Assume the following "template" world (I'm saying it because it depicts an idea of mine, but can be derived to others' worlds too):
- Fantasy landscape, under the control of one god.
- God has direct influence, meaning that inhabitants are universally aware of its existence. In short, they know it exactly as it exists.
- Inhabitants know much enough about God to form an identical and true image of it. Thus, every religion has a common base.
- Magic is based on the same fundamental and universal principles and often used in a similar manner, providing strong transparency between techniques.
- Two or more human kingdoms exist and wage war on each other. All these consist of white people, eliminating chance for major racism, but giving place to minor one.
- There are other intelligent species, varying between hostile and allied ones.
Conclusion: at the very least, human race itself has common:
- place of origin (-> race in both terms)
- knowledge of magic (in basic terms)
- belief in the same deity,
leaving place to only differences in culture & ideology.
My question is: in a world, where so many other threats exist, is there anything that can prevent human race to unify, and go on their own ways instead?