WIY: Under German law, the only thing the Nazis had to worry about was if an eventual court found they hadn’t received valid orders. Some were a bit nervous about it. While the Brits and Soviets just wanted to execute war criminals with minimal trials, the Americans insisted on “due process of law” and ended up largely inventing modern international criminal law. It was quite radical since most western countries had always held that a soldier following valid orders was not subject to punishment.
Halacha is totally different than the goyim’s law. This has been an issue for the Israelis. It may become a very big issue when they start conscripting the Benei Yeshiva in a few months (assuming anyone shows up) – since if halacha as determined by the Bnei Yeshiva differs from what the army says, they will refuse to follow the orders. And if most hareidim regard the situation as “Shaas ha-Shmad”, they will be strict on everything