Why fight Iraqs war?

Why are we fighting someone elses war? Why is it our place to make other nations democratic? If they wanted democracy shouldn't they have banded together and overthrown their own government? Isn' that what a small group of people in a tiny place called America did? Didn' they overthrow a country that was a monarchy? So why are we fighting a war for them when they don't want us there, where they hate us, and kill our good people? I understand that sometimes war is inevitable...it is life. But this wasn't our war to fight. It was theirs.