Second of all, America hasn't had "her share of tragedies", at least not when you compare it to most other countries.
Again, those guys beheading prisoners aren't the Iraqi/Afghan/whatever government. They are terrorists, terrorism isn't an army to fight against. Nor is it a country. They don't even fall under the Geneva convention. Terrorism itself is illegal in most laws.
Now comes the funny part: Of course Iraq had no chance of winning any war against the USA. They never had.
There isn't a country in the world that has the fighting capabilities the USA has. The problem here is, anyone who wants to fight the USA has to use terrorist-like tactics if they want to make an impact. Take Iraq for example, the incredible increase in terrorist attacks since the occupation speaks for itself.