Decision to go to War in Iraq
After 9-11 Bush knew that this event was horrible but he could also use it to increase his popularity by saying how he would "payback" the perpetrators who hurt our country. Bush could then use this war to maybe get more of his other ideas on paper and real like a future war in Iraq. It is fair to say Bush wanted that.
Role of Individual
Being the president, Bush is the Commander in Chief of the armed forces so he obviously has the power to send troops into action. Being also the Head of state Bush could use his figure as a rally point for the country after 9-11 to get people to agree with his wanting to go to Afghanistan.
Afghanistan was a theocratic totalitarian government while we are a democracy. The two form of governments should not really get along since totalitarian is the complete opposite of democracy.
Bush could say that our form of government will benefit the Afghanis more (while getting some payback for us) then the government they have now. Bush could sell the war on the fact both sides would win.
Fear is the biggest point Bush used to go to war in Afghanistan. The point was that if we did nothing our enemies would continue to fester there and get us again later (I.E. Terror Alert Color Code System...keep the fear real and apparent). Of course the American people would not this. It also can be said that the ideals of our country would be better spread to the Afghan people who've been oppressed.
There really were no relations with Afghanistan after the Taliban took over except maybe a few friendly missile attacks by the Clinton administration but...