First invasion? Anybody forgetting the Philippines?
Armed rebels who'd formed a revolutionary government were already giving the Spanish a headache back at the turn of the century (19th to 20th). Then the Spanish had a little fracas with the Americans that turned pretty bloody for the Spanish, and American and Philippine troops pushed them out of Manila.
As part of the spoils of war, they sold the Philippine colony to the US for a nominal sum.
The Philippine independence government accepted the US forces with joy at first... but the American government refused to recognize the Indepence government. There was a pretty short war between the independents and the US after that, ostensibly over three Filipino soldiers killed by American forces. Predictably, it turned out bad for the locals.
Whether the forming of the Commonwealth under US guidance after that was a wise decision or not, nobody can really tell... but it's sad that they didn't work with the Independence government to set up a democracy, and instead decided that they "knew best" what the Philippines needed. Sort of: You'll accept democracy as we shove it down your throats... no, we can't vote on that... we're in charge. Kinda ironic... huh? Still, they did do their job, and they left us in great shape afterwards (although the Commonwealth they left behind has sort of rotted in the past few decades) but that single act has prompted anti-US sentiment for the past hundred years... and it's only gotten stronger since the Marcos era, since they gave so much support to that fascist bastard, merely because he was anti-communist.
The US probably didn't want a military government in charge, but then again, isn't that how the US started, many years ago? A revolutionary government can transition successfully to a democratic government, and, indeed, the leaders of the revolution itself were elected by the members in a general vote, and they drafted a democratic constitution long before hostilities ignited with US forces. If the US had agreed to accept this constitution, maybe they'd have a Philippines completely friendly towards them, instead of the love-hate relationship they have now.
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Diversions aside, the main problem in Iraq was, and has always been, a failure of intelligence. It doesn't take a huge amount of brains to see that guerilla warfare and insurgency would start the moment US troops had settled in, considering a vast amount of Saddam's forces had gone to ground before the US troops waltzed in. Of course, it would have been hard to predict that Al Quaeda would have found such a strong foothold in Iraq after the invasion, but there you go.
Democracy can only really work from within. Of course, from the outside, we think we are only assisting the process... but in the eyes of the locals, any outside involvement is an imposition.
I do agree, that of all the forms of government, it is the one that seems to work best, but it's not a process that comes easy, and takes a lot of time.
That's something people will just have to accept in our dealings with Iraq. There is no quick and easy solution, and no, it's not all love for the "liberators", especially when local political groups have such a huge stake in the outcome of this occupation. If you don't make them feel like they're a part of the process, they'll rebel. The current, shaky, coalition government was a step in the right direction, and the pacing with which the US is trying to help the process along is good... but it's only the Iraqis who can really make it work.
All we can do is help keep the militants and Al Quaeda at bay (since you know the government won't allow more troops or a more decisive action than the one they're taking now) and hope for the best.