Laws, rules, canons of faith.
There is one common thought amongst all people. That there are rules we must follow. What those rules are, is where a great deal of our differences exist.
Jews, Christians, Muslims, Buddhists, Wiccans, etc.. all have differing views/theories/beliefs about God and how to worship him/her.
Americans, Arabs, Africans, Indians, Aborigines, Europeans, Eskimos, etc.. all have differing views of how to society should behave and what is the "correct" or "proper" way to live.
Law-makers and law-breakers appear to have VERY differing opinions as to how their local "Laws of Man" should be followed.
One parent may raise their child following a very "touchy-feely" ideology of parenting, while another may follow the old "spare the rod, spoil the child" philosophy.
Ask a drug addict, and he'll probably say "You haven't truly experienced life, until you've been high." There are people who live every second of their life based on their belief's scriptures.
Any people don't understand how anyone could, or would even want, to live their life as a homeless person. But look at nomads and gypsies; traditionally, they aren't tied down to one piece of property, their life is almost always "on the move".
And the "rules" don't just end with things we choose.
There are physical laws that we "must" follow. I say "must" because many times, there have been things that were, not only accepted by the general populace of Earth, but by "learned", scientific minds as well. "The Earth is flat" was a concept that was thought of as a "scientific fact". What about "The Earth is the center of the Universe"? or maybe just the Solar System? No, not that either. As time goes on, and we learn new facts about the world (universe) we live in, our "absolute, true and unchangable" Laws of Physics, change.
Someday, we will be able to travel through time, someday we will meet extraterrestrial life, someday we will be truly free from death. But until the day when someone proves these to be attainable, we will believe these to be untrue, maybe even "impossible".
The real truth is, the world is what we make of it. Philosophically, spiritually and literally. If we put our differences aside, and accepted the beauty of our varied societal customs, would we be fighting as much? Who cares what you call the piece of land you're standing on, as long as we can share it.
We can change the world with a thought. Don't think so? We do it every day. Our negativity makes the world a meaner, darker, depressing place. When you're happy, the Sun shines, things are good, fortune smiles upon you. Go ahead, give it a try it.