Lord of War would have you convinced that evil always wins, even against overwhelming odds. However, in the real world, Viktor Bout, of whom the main character is apparently inspired from, is currently rotting in an American prison. As it turns out, illegal arms dealers cannot act with impunity with America's blessing and are in fact not appreciated by the U. S. authorities. Now to give the film credit, arms trafficking is a serious global issue and organizations like INTERPOL do suffer from underfunding. Furthermore, Bout wasn't stopped until around three years after this film was made.
The U.S. certainly has a long history of shady (and outright evil) crimes against humanity, however the country's international influence has been more a force of good than the sort of sinister conspiratorial domination that is depicted in this film. In absolute terms, the country's diplomatic methods could be considered "evil," but when compared to the likes of competing superpowers, it behaves benevolently. Mind you, this is all just my opinion.
The film's cynical defeatism does not outweigh what is otherwise a well-made film. Cage's performance and charisma is also a plus - as is the film's good pacing.