> United States using its military to keep international waters open

Being a little pedantic, as per my knowledge, the Strait of Hormuz is not “international waters”. It’s territorial waters belonging to Iran and Oman. AFAIK, Iran hasn’t ratified UNCLOS either, and claims it is not subject to it.

It's prohibited under international law to attack a sovereign nation, like the US has done to Iran, so the point of Iran closing the Strait in response to this is very much moot.

> It’s territorial waters belonging to Iran and Oman.

The trick is that it's still an 'international strait', or a segment of water that forms the only connection between two areas of high seas -- in this case the Persian Gulf and the Gulf of Oman. The principle of freedom of navigation establishes that innocent traffic (civilian traffic, and even warships in peacetime) have a right to use the strait to go from one body of international water to the other.

Iran may claim that it doesn't have to abide by that right, but international law is never self-executing. One question to be resolved by this war is whether Iran will ultimately recognize the right to navigation in any settlement (and then choose to abide by said settlement).

If Iran doesn't want to observe the terms of the UNCLOS (regardless of whether they have ratified it or not) then their territorial waters claims revert to the older 3NM limit. They can't have it both ways. Of course, in practice those legalisms don't matter without a means of enforcement.

> Iran hasn’t ratified UNCLOS either, and claims it is not subject to it.

Which isn't unique. Bunch of countries haven't ratified it and aren't legally bound by it but do follow it in spirit. US, Turkey, UAE, Israel etc.

All straits other than the Bosporus (which has some additional rights to Turkey given the proximity to a major city) are international waters for the purposes of free transit, under the Montreux Convention.

No, the Strait is international waters and always have been.