Once you know how to chain thermonuclear stages, you can obtain arbitrarily high yield without further advances in technology. The Americans pioneered this technique, they just didn't bother building as big of a chain.
At a certain point bigger yields are less desirable than more, smaller yields. Picture an enormous spherical fireball, then picture chopping it up and using the "useless" slices that were at high/negative altitude to instead cover more ground. Once it became clear that they were past the regime of yield scaling, the Americans moved on to developing smaller warheads that could do just that: pepper targets and deliver more devastation per pound than a corresponding single warhead of high yield.
Vanity metrics are always more important to the second place player, and that's what Tsar Bomba was.
That's why the USSR did it. Tsar Bomba is still serving its purpose 60 years later!
The USSR's followup actions give it away, though: they stopped pursuing higher yields, even though there was no theoretical or engineering limit prohibiting them, and instead chased the USA down the path of miniaturization. SLBMs and MIRVs were the future and everyone knew it.
Everyone stopped pursuing them because the massive falloff of effectiveness at higher yields. The explosions got large enough that the difference in air pressure at higher altitudes meant that more and more of the energy released was going straight up rather than directed at the ground.
It's an engineering limit to effectiveness but not an engineering limit to higher yield. I think we agree and are just nailing down the terminology here.
how do you think the missive Tsar bomb was going to be delivered? It would need a bomber which is a vastly inferior method of delivery compared to ICBMs.
The Tupolev Tu-95 is a very nice piece of machinery [1]. Speaking of ICBMs, I also think the Soviets were better at this compared to the Americans, their military had a dedicated Army branch for it, unlike the US.
The framing that I’ve typically seen (from a Western, US-based background) is that the Tsar Bomba was the quintessence of the USSR’s overcompensation for their relatively inferior delivery systems. Bluntly, it doesn’t matter if you’re a mile off target if you create a nuclear fireball a couple miles wide.
The “overcompensation” framing may be true, it may be a bias I’ve picked up from my society, or both or even downright false. In any case, the Soviets established a way to build and demonstrate a weapon that established the threat they wanted. And maybe the CCP will do similar, and get what they want from a path that we in the West will turn up our noses at—but that will still be effective.
