The Star Wars character Yoda once told Luke Skywalker that fear AND aggression lead to the dark side. This is in keeping with this conversation and agrees with the comments above.
While fear certainly leads to conflicts, aggression leads to conflict as well. Greed and avarice can often create conflicts as elements of aggression..
I agree that fear can be "a" cause of conflict, but it certainly isn't the only cause. In fact, often the very lack of fear can cause conflict, as when highly powerful nations attack less powerful ones because the latter cannot defend themselves. Italy did this to Ethiopia, for instance, before World War II, and of course the Germans did the same thing to Poland.
I agree with post 2 that fear can be a cause of conflict but isn't necessarily the only cause. I would agree that fear is likely to be the most common cause of conflict. People fear what the do not understand. It is often this fear that leads to miscommunication, anger, and conflict. Perhaps our worst fears are realized because we are afraid they will be. A person who is afraid that people will laugh at them might become angry when a stranger near them is laughing. The same is true on a larger scale. We might fear that terrorist will attack our country. Suddenly, everywhere we look there are possible terrorists. That seed of fear leads in many different directions.
I would agree that fear is or can be "a" seed of conflict, but I am not sure that fear is "the" seed of conflict. Anger, for example, is clearly also a seed of conflict. We only have to look as far as the local football pitch to see that we people become angry, they often come into conflict.
Fear, however, can certainly be a seed of conflict and has been throughout history. The fear of the Spartans and other Greeks at the rising power of Athens led to the Peloponnesian War (431-404 BCE). America’s fear of additional terrorist attacks after the destruction of the World Trade Center on 9/11/2001 prompted its attacks on Afghanistan and Iraq.
Surely fear can also be a seed for lack of conflict. After all, some people, when frightened, run away.