After the terrorist attacks in the United States, President George Bush started a war on terror, a war which main purpose is to finish any kind of threats all over the world. According to President Bush, Saddam Hussein with his anti-American sentiment and the "possession" of biological and chemical weapons was one of these threats. The proposal of a new war against Iraq came from George Bush. This war was supposed to be based on the core goals of American Foreign Policy (The 4 P's).
Power: Iraq was considered as one of the biggest enemies of the United States, more than the country itself; the enemy was its leader, Saddam Hussein. An active threat could not only harm US allies in the Middle East but also other countries in the world, even America. The risk was too big and some actions should be taken. America should protect itself and its interests.
Peace: Iraq could also deter world peace as it did before. Saddam Hussein's greed and power could result in another invasion to a Middle Eastern country. The United States had also a big responsibility in this aspect, as one of the most powerful countries in the world, it was necessary an US intervention in order to preserve the world's peace. Even though the United States was breaking the peace by going to war against Iraq, this war was necessary to avoid a bigger disaster.
Prosperity: The economic national interest was also involved in this war. Iraq has the second largest oil reserves in the world, but also Iraq's neighbors, like Kuwait, are important oil providers to the US. Since the safety of these countries was in danger America should protect them, and at the same time protect its own economical interests.
Principles: Saddam Hussein was a brutal dictator who committed mass murder against his own people. There were no civil rights in Iraq, repression and tortures were common denominators in the country. George Bush also wanted to bring freedom to the Iraqi people and all the rights that were taken from them.
After the war was over some of these goals were not achieved, totally. The main reason to start this war was Saddam Hussein's possession of biological chemical weapons. These weapons or any proof that they existed have not yet been found. Peace was also broken, and even months after the war is over and Saddam Hussein has been captured, there still is not peace in Iraq. Many innocent people died during this war, and today people are still dying as a consequence of that war. The United States violated several provisions established by the United Nations. The US was supported by some countries but it was not the same number of supporters as in the first war against Iraq. The UN and countries like France did not give all their support to this war.
On the other hand, prosperity and principles goals were achieved or are on the road to be achieved. The US provides more security to many oil producers in the Middle East and it will also gain a new provider, Iraq (This is the reason which I believe the war started). Also democracy is on its way to be established in Iraq; people are recovering many of their rights and freedom. As Jentleson explained in his book sometimes some goals have to be sacrificed in order to achieved the others.