The war veterans in my life (father, uncles, grandfather) have always said that a just war is when we defend ourselves, but don't start it. Everyone has the right to defend themselves if attacked. But the next question that pops up for me in my lifetime is our invasion of Iraq in 2003. We hadn't been attacked by the Iraqi people; but, is it just to attack first when there might be evidence of a future possible one? Is it better to be wrong and protected than right and invaded? I think that for myself, I'd rather hurt before getting hurt if diplomacy has completely been tried and failed beforehand. Negotiations and diplomacy first, though!

I suppose in this sense “just” means right and fair.  I don’t think that’s a valid distinction.  There are good and bad things that happen in every war.  People can do unjust things for just reasons, and just things for unjust reasons.  I think a war is unjust when it is just a grab for land, like the wars against Native Americans.  Yet the Civil War was fought for what seems like a just reason.

Theories of what constitutes a just war have changed over time, and so have the implications of these theories. For example, some people argued that slavery was acceptable as long as the slaves in question were captured in a "just war." A "just war" in the seventeenth century, for example, was one against an enemy that practiced cannibalism, human sacrifice, aggressive wars, or other practices that were contrary to European mores. This concept was used to justify the purchase of slaves from Africa (which were captured, it was said, in "just wars" against other nations) and the taking of Native Americans as slaves. Later, Western thinkers argued that just wars were those undertaken in self-defense, or to punish a party guilty of aggression or other violations of international law. It should be noted that there are two sides to just war theory, however. Jus ad bellum describes the right to go to war, and Jus in bello describes proper conduct within a war (such as conduct toward prisoners, proportionality, avoiding civilian casualties, using conventional weapons, etc.)

The previous post provides a good example of the unjust invasions by Hitler that inititated World War II. Other more recent examples can be found in Africa and Eastern Europe by wars brought on primarily to eliminate rival groups--"ethnic cleansing."

This depends, of course, on your point of view.  Most of us would say that World War II was a just war on one side and an unjust war on the other.  Germany and Japan were not justified in starting the war for territorial gain.  The Allies were justified because they were just defending themselves against aggression.