That may not be but this is. Children born of one Israeli parent outside of Israel in any country have automatic Israel citizenship and both sexes are required to serve in the Israeli military. Those born and living outside Israel get deferments as long as they don't come to live in Israel.

All U.S. citizens with dual Israeli citizenship are free to go serve in Israel's military. This is because it's mandatory if they live in Israel, which makes it conscription, and being conscripted does not violate U.S. law. If you go to Zululand or ? and get forced into military service, you don't lose your citizenship.

Whether non-Israeli , U.S. citizens can legally serve in Israels military, I don't know. However, there is this: 163 U.S. 632 (1985), the Supreme Court endorsed a lower court ruling that it was not a crime under U.S. law for an individual to go abroad for the purpose of enlisting in a foreign army. I do know that in WWII, many of our citizens went to England prior to our entering the war and enlisted in the British military and were honored for it.

Where U.S. Law seems to come into play in this issue is that you can't legally join a foreign military service while still in the U.S.. You have to go to the other country first, to do it.