War is not a necessity, we do not need war. War is inevitable. Whether it be a president, a dictator or a tribal chieftan any sizable group of people will put someone in control. Then, when groups meet the leaders will send their pawns to go fight. This is human nature.
War is too powerful of a tool for governments to ever let go. War is a means of obtaining what one wants without making it themselves. War is a means of instilling fear in your people, or hatred of the enemy thus keeping the people looking to the leader for protection and keeping their attention off of the leaders' own evils.
People banding together has not and will not eliminate war. Just look at the 60s. How popular was it to protest the Vietnam war? We didn't get an end to war out of that, just some good music, a lot of pot and the hippies who later turned in their ideals and became the yuppies.
The serfs did not wake up one day and throw off their monarchies. The monarchs became to secure in their positions. They allowed some families to become richer and more powerful then they were. These families along with some free minded "serfs" (there are always a few rare ones) stirred up the people and eliminated the monarch threat to their own position. Now they exist today in the form of the corporations and political parties which are slowly chipping away those freedoms returning the "Free World" to our more natural less free state.
Democracy is not a new idea which is suddenly sweeping the world. Democracy has existed at various times and places such as Ancient Greece and Rome. Yes, some parts of the world are currently becoming more free but surely by the time that the current dictatorships, monarchies, etc... are all replaced with democracies many of the existing democracies will be replaced with dictatorships and monarchies.
I only hope that mankind starts colonizing frontiers on other worlds before society on this one becomes so tightly controlled that natural selection starts taking away our brainpower and makes our descendants collective like ants. That I'm convinced is the future on this world. Only in open spaces where we can expand too thin for central control does human nature tend towards freedom.