Rees-Mogg actually lied through his teeth in that part of the interview: he claims that, in a treaty, America "guaranteed" Ukraine's territorial integrity, making it "inviolable", as a "quid pro quo" for giving up its nuclear weapons.
This is completely false.
The treaty he refers to is the so-called "1994 Budapest Memorandum", whose full text you can read here:
nsarchive.gwu.edu/sites/defa…
What the U.S. (alongside Russia and the UK, the other signatories) did commit to is "to respect the independence and sovereignty and the existing borders of Ukraine," to refrain from the threat or use of force against it, and to refrain from economic coercion.
These are promises about each signatory's own behavior: the US promised not to violate Ukraine's borders ITSELF, it did NOT guarantee their inviolability against anyone else - contrary to what Rees-Mogg is saying.
Steven Pifer, one of the US negotiators, wrote about this in an article he titled "Budapest Memorandum Myths" for Stanford's Center for International Security and Cooperation (
cisac.fsi.stanford.edu/news/…). He writes that the claim that "the United States and Britain violated their Budapest commitments by not going to war against Russia on Ukraine’s behalf" - what Rees-Mogg is essentially saying - is "a myth."
In another article he wrote for CNN in 2014 (
edition.cnn.com/2014/03/04/o…) the same Pifer explains that "U.S. negotiators — myself among them — discussed this point [i.e. the absence of security guarantees] in detail with Ukrainian counterparts so that there would be no misunderstanding."
The only thing the U.S. (and the other signatories) committed to do if Ukraine was attacked was "to seek immediate United Nations Security Council action to provide assistance to Ukraine" - and even that only in case of an aggression "in which nuclear weapons are used."
And the U.S. did go to the Security Council, but given that Russia is a permanent member of the same UN Security Council, it's of course completely useless.
Rees-Mogg is also lying on the other half of the supposed "quid pro quo": the fact that Ukraine supposedly agreed to get rid of "its nuclear weapons," emphasis on the "its."
The nuclear weapons on Ukrainian soil were never theirs to keep, and they never had operational control of the weapons: the launch authority was always in Moscow and, even if Ukraine had wanted to launch the weapons, they couldn't have because they didn't have the launch codes.
As Ramesh Thakur, former Assistant Secretary-General of the UN, explained in a 2014 article titled "the myth of Ukraine’s nuclear deterrent" (
opencanada.org/the-myth-of-u…), the bombs on Ukraine's soil "were always Russian bombs that happened to be based in Ukraine" and "were not in fact Ukrainian, any more than NATO nuclear weapons stored on West European soil or U.S. bombs that used to be kept in South Korea belonged to the countries on whose territory they were located."
So there you have it, Rees-Mogg is your classic Eton-educated British politician: extremely posh and very well-spoken, supremely confident in everything he asserts, and... a shameless liar, peddling thoroughly debunked myths.