Why countries engage in war?

The sad truth is that it's in people's nature. Everyone wants to dominate the rest. Those that are the dominant members/races of society have to continually defend their position by fighting and those that are the less powerful members/races continually fight to achieve dominance. In the end every side thinks that they are the "Good Guys" but all they are really doing is conforming with the most primal instincts we have, contained within the reptilian part of our brain which is located at the base of our brain, right where it meets the spinal column.