Have you ever studied history? This conflict, and others, in the Middle East have been going on for thousands of years. Why should it be any different now? You can't possibly believe that people today are any different than those of 3000 years ago. People are people and they always will be.
I am not a pessimist, I am a realist. Conflict is built into human nature. There have always been conflicts/wars/violent disagreements and that will never change as long as humans exist on planet Earth.
Let me propose a couple of scenarios.
Scenario 1. Humans colonize the planet Mars, assuming that Mars is colonizable. The colonists, after many generations manage to terraform the planet and make it a nice place to live and don't need anything from Mother Earth. The Mars colonists, now called Martians, decide to seceed from the Earth-Mars alliance. The powers that be on planet Earth don't like this because there are resources on Mars that they want or need, and besides, didn't they pay for the colonization of that piece of rock 125 years ago? So Earth sends the Earth Alliance Space Fleet to surround Mars. Earth demands that the Martian government turn over control of the planet to Earth. The Martian government refuses and warns the Earth fleet that is threatening them to back off or else suffer the consequences. The Earth Fleet commander decides to teach the Martian upstarts a lesson and wipes out a couple of their cities and about 1/3 of their crops.
The Martian government retaliates by blowing a few Starcruisers out of their ionosphere. The Earthfleet commander gets pis$ed and orders 200,000 Space Marines to invade various tactical points on the planet. The Martian military mobilizes its defense forces to repel the attack.
And you have an interplanetary war.
Scenario 2. In the year 2012 Seti makes contact with a non-terrestrial species. These aliens didn't know that we were here, way out on the edge of what we call the Milky Way Galaxy. Following several years of finding a common language that both the Earthlings and the Aliens can understand it is agreed that the Aliens will send an ambassador to Earth to cement relations between the races. This is because Earth, at this time, still doesn't have the technology to leave its own solar system. In the months that ensue waiting for the Alien fleet to arrive the military commanders and most of the people of Earth begin experiencing some trepidation at having invited a technologically advanced species into their solar system. What are their true intentions? Suspicion runs rampant. The United Earth government decides that it would be better to be safe than sorry and makes preparations to blast the Aliens with hyperspace anti-matter missiles before they enter our system. The Aliens, who may or may not have had friendly intentions, retaliate by taking out several of Earth's major cities.
And you have intergalactic war.
It is human nature to be suspicious. It is also in human nature to always want more, to believe that "their" way is better than "your" way and they are willing to kill you to prove that they are right.
Nothing has changed since the beginning of time and it never will when it comes to human nature.