The world was a very worried place in the early noughties, and people had witnessed the worst terrorist attack ever only a few years earlier, meaning they were very aware of the damage that could be done to people when they were a long way away from any war. So, when hearing that Hussein was creating weapons of mass destruction, they immediately say him as a threat to the west, and so did our leaders. Since the first gulf war we had been keeping an eye on him, and WMDs certainly meant trouble, meaning people felt justified in attacking a country that was a threat, since that was simply defending ourselves.
In addition, the west had become rather obsessed with removing Hussein from government. He was a dictator, and like many dictators, found oppression to be something necessary to stay in power. People were not allowed to say what they wanted under Hussein, and political freedoms were negligible. Many argue that, if all else fails, at least the war was a good idea in that it removed a despot from power, someone who, as Tony Blair pointed out, could have caused devastation if the Arab spring had arrived in Iraq when he was still in charge.
Yet, neither of these two factors really cut it. Firstly, because it turned out that there were no WMDs. Even before the war it seems like there was very little threat from a nation that was very aware that it would lose any war against the west. Some within the western intelligence agencies felt differently, and very poor decisions were made on little evidence. We invaded the Iraq just in case, without nearly enough evidence to say that it would be a good idea.
Also. the situation in Iraq is not that much better now. There has been significant improvements in some areas, like being able to say whatever you want, but the Hussein regime has been replaced with what it described as one of the most corrupt governments in the middle east. One problem has been replaced by another, something made worse by the fact that sectarian violence has flared since the fall of the old government. 111,827 people died in that war, and nobody really knows why it happened. That is hardly justifiable, and far from a good idea.
If you look at a graph of when the causalities occurred, you will see that the worst years were 2006-2008, several years after the invasion. Iraq descended into a dark place that manufactured terrorism and violence. As much as a threat was removed, another was created, at the expense over 100,000 people. This is not justifiable, this was a mistake. This was not a good idea.
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