As we all know, humans have a natural tendency to break off into groups who share common interests and attitudes. There's nothing inherently wrong with that. What comes next, however, is trouble.
No matter what kind of organization you're in, it's only a matter of time before these groups start fighting amongst themselves. Sometimes it's a matter of competition for a particular set of resources. Other times it's a struggle for dominance. Often this discontent is driven by petty warlords who sit atop their little tribe and dream of ruling the entire kingdom, or at the very least obtaining more cows.
Even without a leader stirring up trouble these groups will still grind against each other. One of the most prominent reasons for this is cultural clashes. For example, in the typical modern day corporation you'll have a department of techies who manage computers, software and other such necessities. Another group that's a constant in any for profit business is that of sales and marketing. As you might imagine, these are two departments with a very different lifestyle and world view. Imagine yourself at a party where they happen to be in the same room and you'll have a pretty good idea of what goes on each day in the workplace.
Whenever there are three or more people in a room, you're likely to have politics. It's often more emotional than rational and many times is little more than gossip about some other person or group. Other times it's driven by ambition and the quest for wealth, power and status. Further, where there's politics and ambition there's going to be more than one person involved, as those seeking to rise to the top need supporters to get them there.
Regardless of the management style you adopt, tribal conflict is a constant threat. It's still just human nature but on a scale that can derail everything you've worked to accomplish. Ignore it at your peril.