Who and what comes after Putin? I can more easily see China trying to seize parts of Siberia - sparsely populated and rich in natural recsources which the Chinese need and are better positioned to exploit - than China going to war with us. They can always go to war with us later, watching us weaken year by year.
That's his biggest flaw. He needs to nurture a successor. But the problem is that he is probably too paranoid to do that.
I can more easily see China trying to seize parts of Siberia
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That would be a fatal mistake and Xi knows it. One troop crossing the line and good bye Beijing. Xi does not want to repeat the mistake of ‘69, and Russia will use nukes to stop them.