critique:  More than half of bitcoin mining takes place in China, therefore, China can seize control of the Bitcoin network at any time.

rebuttal:  While it's true that mining pools in China currently generate a large portion of bitcoin blocks, it's important to understand a few factors at play here: 1) mining pools are very dynamic entities that can and do change fast in response to network or political conditions, 2) a 51% attack is not the same thing as 'control of bitcoin', and 3) as the mining market grows and matures, it is shifting more and more to places outside of China.

First, it's important to understand how the bitcoin mining ecosystem is structured. Most hashpower is aggregated by mining "pools". Pools are composed of many smaller miners who use pooling software to logically aggregate their hardware towards working on the same block at the same time. Individual miners within a given pool can be physically located anywhere. If anyone in the pool finds a block, the profits from that are distributed to all pool members pro-rata according to the hashrate each member contributed. This is the standard approach to bitcoin mining, since miners generally want smoother income in the face of bitcoin-mining's volatile statistical process.

A key aspect of pooled mining is that while it is time-consuming for miners to move or deploy equipment, it is trivially easy for most miners to switch pools - it is usually just a one-line software configuration change. This means that mining power is actually much more functionally diffuse than it might seem at first glance. Furthermore, it means that miners in aggregate can be very responsive to political threats. For example, single mining pools got close to 51% of hashpower in 2011, 2013, and 2014, but the legions of individual miners that comprised those pools switched to other pools when that 51% threshold was getting close. They did this due to the perceived threat of one mining pool having 51% of hashpower combined with the fact that it's trivially easy to switch pools.

Of course, this is not to say that China isn't the jurisdiction with the largest portion of hashpower, but it does suggest that it may be a lot more difficult in practice for the Chinese government to seize control of mining equipment than some might assume.

Furthermore, control of hashpower does not confer control of the bitcoin network. An entity that controls more than half of bitcoin's hashpower could in theory disrupt the network, making it difficult or impossible for normal transactions to confirm, but such an attacker could not steal funds, for example. Ultimately a 51% attack could in theory be mitigated by a hard-fork to the bitcoin protocol. This would have severe impact to the bitcoin mining market, making all previous ASIC equipment useless.

As for trends in geographic mining distribution, it's difficult to get good data, but the Cambridge Centre for Alternative Finance collected and published mining data during parts of 2019 and 2020 that sheds some light. According to the most recent datapoint provided there, 65% of mining activity is likely to have taken place within China in April 2020. That's down from 75% just six months prior. It's reasonable to assume that this trend has continued as China has become less politically hospitable to miners recently, plus North America has seen something of a mining boom in the past year as various projects have become economically viable. In fact, Mustafa Yilham, VP of global business development at Bixin (an Asia-based mining firm), recently commented on this on an On The Brink Podcast episode:

"So, you know, price, regulation, temperature are like the most important factors. I think Central Asia is great for mining outside of China, speaking in Central Asia is great. Russia, I think have huge potential. North America, I think has the probably most potential in next few years, for a few different reason. But I think those are generally the regions we look at when I sourced electricity"

"So, I think based on our conversation with different mining manufacturers, on average, right, like around 60%, of the mining machine sell in past two quarters or so have been outside of China, in recent months, and mostly actually in North America. And I think that there’s few factors that plays into why North America could be huge in mining in future. One of them is price. I think you’ll be surprised to hear that. In fact, the price right now in North America notice are cheaper than the average price in China."

In short, it's much harder for China to seize and control mining equipment than is usually assumed, China couldn't do more than disrupt the network if they did so anyway, and bitcoin mining is rapidly becoming a much more distributed global enterprise.