The Constitution allows for private intervention to be permitted by the Congress through the Bill of Mark or Retribution. In semi recent history, a large number of motivated americans supported the Republican effort in Spain. Quite legally a large number of American Jews have and do serve in Israel. Private contributions and loans from American Jews support Israel. Imagine how much more secure Israel would be if American Jews, and concerned Christians paid no income tax to support mismanaged military adventures. I worked for the US Army for 7 years. It is managed as well as every other socialist enterprise.