Why do so many believe that American lives are worth more than the lives of poorer countries that we invade?

So 9/11 happens where most of the hijackers were from Saudia Arabia and about six thousand people die, which is horrible and I do believe we needed to retaliate in some way. So we invade Afghanistan to find Osama Bin Laden we have him cornered ask for more troops so we can either kill him or detain him and the government refuses. We then plant ourselves in Afghanistan for the next ten years and fight men in caves and people who are poorer than we could ever imagine. At the same time we invade Iraq for whatever reason and kill hundreds of thousands of Iraqis who had nothing to do with 9/11 or any other terrorist network but feel it is necessary for "democracy". So, the more people I talk to the more I hear "well they attacked us first"...When most people don't even realize who attacked us and why. It's almost like people believe that since thousands of people died here in America on 911 that we need to kill hundreds of thousands of more people to equalize everything. None of this makes sense because how can you attack a country that had nothing to do with your country being attacked? That's like someone killing my sister but then I kill a random person because someone had to pay the price. So why do I get the feeling that people in America or westernized countries believe that not all human lives are equal and that 1 American life is worth 1000 Iraqi lives? Again, 911 was a terrible day and I am not trying to be anti American about it, but I think we went in the wrong direction after those events transpired.