Seemingly there are myriad sources of conflict, but the essence of conflict is simple. All conflicts arise because you can't see how to get from point A to point B.
Point A is your present situation that you wish to change. Point B is the potential future situation where your goals, needs, wants, or desires are fulfilled.
If you clearly see your path, there is no conflict. If you are confused and lost, frustration slowly (or quickly) grows into inner conflict.
When you find a similarly conflicted individual, drama and outer conflict are quick to develop. At that point, any of the superficial sources of conflict (excuses really) can serve as a trigger for the conflict.