First, China, despite being an economic powerhouse, isn’t in a position to supply some things Russia needs, like spare parts for Western-made airplanes and high-end semiconductor chips.

Second, while China itself isn’t joining in the sanctions, it is deeply integrated into the world economy. This means that Chinese banks and other businesses, like Western corporations, may engage in self-sanctioning — that is, they’ll be reluctant to deal with Russia for fear of a backlash from consumers and regulators in more important markets.

Third, China and Russia are very far apart geographically. Yes, they share a border. But most of Russia’s economy is west of the Urals, while most of China’s is near its east coast. Beijing is 3,500 miles from Moscow, and the only practical way to move stuff across that vast expanse is via a handful of train lines that are already overstressed.

Finally, a point I don’t think gets enough emphasis is the extreme difference in economic power between Russia and China.