I am 18, and last summer when I finished high school I went to a recuiter. When I was nearing signing the final papers I did some research and found the US could force me to wear a UN uniform, I backed out of signing up right then. I will not serve any country, or fight any wars, but this country's. If you want to fight a tribal war suite youre self, but never force another man to give his life for a foreign conflict that does not concern us.
This is why my version of the universal draft would only be for training and into an organized but non federlized militia. The militia, under the constitution, can only be called into federal service to quell insurrection and to repell invasion. The National Guard is not the militia, although it's members are indivdually part of the miltia of course, which is why the Guard can be called up for overseas duty, and even ordered overseas for annual training. When I was in the Air Guard, my ID, red then, but now they are green like active duty, was exactly like that of the federal military reserve, which I also was a member of both before and after being an Air Guardsman, I don't recall needing a new ID when I transferred from Reserve to Guard. In fact Guard members are part of the federal military reserve, except when used on state missions such as disaster relief. The so called dual hatting fiction, which just means that a states guard unit can be loaned to the governor when he needs it and the Army doesn't. This is not true of State Guard forces, which many states have. Some, Texas and California for example, even have state Air Guards. These state guards could be vastly expanded into true militia outfits.
Guard members would of course be able to voluntarily serve overseas, even entire units could do so, which is pretty much what happened during the civil war and to a lessor extent in WW-I, before the Guard was a much a federal institution as it became after WW-I.