perfidy

International treaties that have been given the thumbs up by the senate have the force of law - they are not part of the constitution, any more than a regular statute is part of the constitution. A simple senate vote could pull us out of the Geneva convention (not that we should.) There is some debate on how treaties should be interpreted, and that is a matter for the supreme court - but there is no question that a treaty can not invalidate part of the constitution itself. The ICC treaty would violate the fourth, among others. No treaty could remove the right to bear arms. 

International laws of war, with the exception of the Geneva convention, are rather amorphous. And the Geneva convention deals largely with issues of POWs and the like. There are no treaties, just precedents, and arguments.

The general militia is not the first line of defense. The Constitution provides for an Army and a Navy. If some foreign power can fight their way through that, (hard to believe) *then they'd have to deal with the general population, half of whom own guns. Would you want to attempt to occupy a nation where half the people own guns and don't like you? Even in hellholes like Somalia and Afghanistan, gun ownership is not that prevalent. The general militia is the last line of defense, just as it was in colonial times. (Though more often called into action then.) It is the last line of defense against foriegn invasion, and against domestic tyranny. Of course, the first lines of defense are free press, free speech, elections, democratic institutions, the constitutional amendment process, and the general habits of living in a free soceity.