1. You have to start from somewhere. In the north they border Russia which is strong and hostile to them using it for destabilization and extremism purposes. DPRK border is also out. Mongolia is a possibility but I’m guessing they just haven’t managed to do anything there, maybe the soil simply isn’t fertile for extremism and color revolutions. The best place adjacent to regions they’ve long been fomenting extremism, separatism, terrorism in is via Xinjiang for that reason of geography alone. Fact is after Afghanistan which many IMO rightly see as a move to get closer to China for destabilization operations (though I do think some neo-cons at the outset genuinely thought they could create a stable westernized puppet there to blunt China and provide a nice staging ground for the US military in a war against China).

2. Islamic extremism is a tool they’ve used since AT LEAST the 80s against the Soviets in Afghanistan and to great success, many planners in the west I think see that moment as a big turn-around, a win at last off the back of a long streak of losses for the west in proxy conflicts like Vietnam, Korea, etc. Regions of China without Muslims wouldn’t be vulnerable to that type of extremism. I do see some history there of them trying to rile up Christians and using missionaries as they always have but China cracked down on that quickly and to my knowledge there aren’t any regions that specifically have a very large Christian minority or majority population and there’s not an ethnic angle there to work along-side that either.

3. Belt and road goes through Xinjiang. You destabilize that you destabilize any hope of land power and transit except via going around the very, very, very long way through the north of China, through the length of Russia, etc and at that point Russia is holding all the cards not China which isn’t exactly to the liking of China and also at most allows it access to Europe not to the rest of Asia, to west Asia, etc.

4. In one of the most influential public policy documents ever released called The Grand Chessboard by Zbigniew Brzezinski (the father of the Morning Joe co-host but really an important executive/state dept imperialist ghoul in his own right) notes the imperative for the US to establish and manipulate a strategic “triangle of control” that exists in west Asia/the middle east. That via this larger region encompassing multiple countries lies the possibility which must not be allowed to come to pass of land power that would completely neutralize US/NATO naval dominance and might. Specifically a desire to prevent uniting economically in trade the East (Asia), the North (Russia), Europe, and Africa. The crossroads human trade between all of these, of power, of military movements is the middle east. Control that or at least deny it to your enemies, keep it so unstable as to be impossible to route trade through, to have military alliances through and you keep these disparate powers of Russia, China and Asia, Africa, and Europe the EU from uniting into a bloc whose power would crush the US and exclude it, leave it an ocean or two away isolated and losing power and relevance. So anything that threatens to export prosperity, trade, stability and peace to that region is a threat to the US strategy.

5. A distraction and whitewashing of their own past. After Bush the US rightly became widely hated in the middle east by peoples there-of for all their invasions, violence, etc, etc. They need to re-frame themselves as bad in the past, good now versus China being framed as the bad one now to direct the hatred of those peoples against them. This is more of a bonus than an imperative compared to all the much stronger forces but the US does maintain dominance via very strong propaganda and messaging that sells even to its enemies that they are good people, that you should aspire to be like them, etc.

IMO that’s also why Tibet was targeted, it was fertile and they did want to help the former slave-owners get their slaves back and establish a loyal puppet and would regardless of who ran China or how but it was also in China’s west and a way of starting to cut them off, to isolate them, to encircle them and then turn up the heat. And it was of course fertile ground because of the existence of a sizeable ethnic group that’s different from most eastern Chinese ethnic groups. The western plan has always been to encircle, isolate, sanction, and turn up the heat and pressure until a major power cracks. It was their thinking against the USSR, against Russia, etc. They have this containment mentality and China knows this which is why fostering trade routes has been an imperative because they’re rightly desperate not to let the US do this as it could allow great economic pain being inflicted on the Chinese people which could be enough to bring down the CPC as despite the fact Chinese citizens get lessons in Marxism in school, they exist and since opening up have exposure to a capitalist global culture dominated by the US.