What happened during the XXth Century?

A Serb anarchist kills the Austrian Archduke and because of alliances, WW1 starts....badly concluded, which caused WW2.
90 Million deaths.
Yes, true, those wars enabled a huge technological progress, cheap flights across the seas for millions, the conquest of space.
Technologies on both sides were relatively similar and both sides were extremely motivated to beat the other, using technologies.

WW2 lead to the UN and to a fundamental principle (which Hitler had violated): non interference in internal matters of sovereign nations.

WW2 also lead to the Cold War, decolonizations and the EU.
The Cold War lead to a freeze in wars because technologies enabled mutual assured destruction and the atheist soviets (a little ironic sarcasm, here) didn't believe enough in god to believe they could afford to attack the first and win. So, the cold war thawed and the EU got much bigger!

In all that context, Bush decides to invade and occupy a country that had nothing to do with the worst terrorist attack against the US. Remember, WW1 also started because of terrorism. Iraq has nowhere near the technological level the US had (therefore, very little technology was to be gained) and yet, it manages to bring hell to the troops, the politicians and americans in general.

This is a lesson the US should have learned from previous wars: you know when they start, especially if you do it; you don't know when they'll end!

Wars are the worst thing humans can do; not only because of the loss of lives, the costs, but also because of their complete unpredictability.
Terrorists have ruined the occupied country.

Former enemies ally themselves while the occupier had wished one of them had remained the enemy (Iraq-Iran).

None of those countries show any sign in wanting peace with Israel.
Oil prices go up and up.

When you start a war, you might not even be able to win the peace even if the war isn't really lost.

Wars are no fun.