Thanks for the detailed reply.

Strictly speaking, states cannot be friends; only people. Therefore, the comments by @PrincessLeiasCat@sh.itjust.works and @seejur@lemmy.world must be understood figuratively.

Of course, which I would interpret as, say, allies, or perhaps ideological siblings. The two states were clearly neither. They were enemies on both counts, even well before the war, despite any trade or pacts. I'd say they were no more friendly than the US and the PRC.

You're right that the treaty was not merely non-aggression and had major implications with spheres of influence in the space between the two powers, it was only non-aggression between the signing states (the two being called 'friends' in this context). I don't really know if there was any good ending possible for the countries between the two, because I believe war there was inevitable given the Nazi regime's ideology, expansionist policy and military strength. Those countries, unfortunately, were either going to be occupied by the Nazis or the USSR in the inevitable war, so the USSR made a choice in its self-preservation interest to gain power. Given that the alternative was further expansion of the Nazi regime, it's hard for me to realistically criticize it, despite the horrible implications for the occupied territories.

First, it is not and was not at the time clear that the entire West wanted the Soviet Union and the Third Reich to wear each other out; instead, it was a Soviet belief [...] That belief was questionable. The fact is that the West allied with the Soviet Union and supported it, through Lend-Lease and other means, after it was betrayed by the Third Reich. Of course, hindsight is hindsight, and Soviet leadership did have reasons to believe the West wanted them to fight against the Third Reich, but their assessment was fatally flawed and led to much suffering, not least amongst their own citizenry.

While I say this naively, Western support of the USSR doesn't contradict the theory that the Western powers wanted the two to wear each other out. Supporting the weaker side wears out the stronger side more, this is an established tactic in proxy warfare.

Second, you ignore Soviet agency and deflect Soviet responsibility to the West when you describe the Molotov–Ribbentrop Pact as “realpolitik compromise resulting from the Western powers wanting the two countries to destroy each other”.

That wasn't the point of the line, I was emphasizing that the Soviet's first choice was to ally with the West. It's misleading for the poster to consider the Molotov–Ribbentrop Pact as a signal of the USSR's alignment without acknowledging that they first tried to create pacts with the Western powers against the Nazi regime. They were rejected, and the USSR compromised and created a neutrality pact with the Nazis because the alternative was to be invaded first. At that point, what agency remained? To me, it seems like the options were 'form a neutrality pact and gain an opportunity to build your defenses' or 'get invaded first and probably die'. The first option was horrible too, but I don't know of a better choice they could have reasonably taken after being rejected by their first choice of allies.