The Hague Invasion Act
m.wikipedia.org
m.wikipedia.org
Whether you support it or oppose it, this Act makes perfect sense, given the US position that it does not recognize the sovereign authority of The International Criminal Court at The Hague.
Since this court does not have legitimate sovereign authority over the United States or it's citizens, this Act is necessary to protect the United States from the court exercising its claimed authority over the US. It is a declaration that the court seizing US servicemen would be treated by the US no differently from how the US would treat any other political body taking their troops as prisoners.
No, it doesn't, because:
(1) The ICC doesn't claim “sovereign authority”; to the extent it relies on sovereign authority it relies on that of the parties to the Rome Statute, whom, nearly without exception, the US does recognize, and
(2) The ICC’s jurisdiction is derived from its Rome Statute members exercise of widely-recognized, pre-existing universal jurisdiction over war crimes (which the US accepts, exercises, and has actively supported other countries in exercising, both directly and through ad hoc international tribunals.)
The Act is based on pure exceptionalism, specifically, that universal jurisdiction is premised on the inadequacy of process of the entities which would generally, either by command authority or territorial jurisdiction, have primary jurisdiction, and US institutions always, by virtue of command authority, are among those with primary jurisdiction over US service members and are, by definition, incapable of inadequacy, and thus notwithstanding the general validity of universal jurisdiction over war crimes it can never validly be applied to US service members.
"International Law" isn't a real thing, because there's no single body with the necessary monopoly on force to implement and enforce it. There is merely the cooperation and posturing of a variety of powers who use a combination of influence and force to secure their interests. Sometimes, nearly all of the major powers agree on something, and then it gets written up and followed closely enough to look like law, but it isn't.
(One could make the same argument about individual State laws in places where the State is either too weak or too corrupt to actually enforce their laws in anything resembling impartiality, but that's beyond the scope of this topic I think)
Why are the rules different if they're accused of a war crime?
The US does not recognize the sovereignty of the International Criminal Court over any territory, and it claims authority in all territory worldwide. Therefore, the US has an official policy of using force to compel the ICC to release American service-members in the event that The Hague attempts to use its authority against American interests.
And part of the inherent nature of authority is the ability to delegate that authority; it's absurd for the USA to accept that Vietnam has jurisdiction over crimes committed in Vietnam but threaten to go to war if Vietnam asks the ICC to hear a charge rather than having it heard in Vietnamese courts.