Consider this: China can close their economy tomorrow and most of the world’s economies would crumble almost overnight. The supply chain of most developed and developing nations is primarily based in China. It would take decades in a developed country to build manufacturing capabilities at the scale China has currently.
Despite being the second largest economy of the world, only 4.3% of international trade happens in in the Yuan [1]. People do not want give their oil and wheat in exchange for Yuans! Countries do not see the Yuan as a valuable reserve currency, which reflects their trust in the Chinese system. Since the majority if international trade happens in US Dollars, China needs to trade with the US to get Dollars.
The US on the other hand produces much more food and energy it needs.
For now. The yuan is still a new currency in the world trade. The Chinese are just starting to push it as a global currency. This will take some time, but I imagine that 20 years from now the yuan will be a second, if not the first international currency.
What's your point? The only reason to point what would happen if China did close would be to show that they have leverage over the rest of the world. But if they can't or won't close, and everyone knows it, then they don't have leverage.
China would be severely affected by such a measure as well. This is WTO's doing, and is a big reason why there has been no world war 3. It's easy to wage war if your economy is truly sovereign, but with a nation your economy is intertwined with, it's hard to wage with. Trump's anti-China policy, while it is sensible in many ways, could have the ill effect of enabling a major war in a few years.
The difference is that mutual defense pacts (WW1 alliances) are very different from trade agreements (modern alliances).
If you have a 1-year stockpile of food, produce only enough food for 50% of your population to not go hungry, and depend on imports to make up the slack, that is a dampening force on the decision to go to war.
These agreements are now negotiated at the national level in trade agreements, and at the international level by the WTO. It's a very different system from the one that existed prior to WWI.
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Although, that's not to say that trade did not play a role in WWI!
Incidentally, the German pre-WWI german economy was dependent on migrant labor from Poland and Russia to exercise successful harvests in Prussia. When WWI broke out, they were not able to replace these migrant laborers in the fields, and experienced crop failures.
This led to significant food shortages during the war, signaled by large increases in the price of bread, in particular.
The military elites (Luddendort, Hindenburg) of the country must have known why prices were rising (because there was a gaping hole in supply), but successfully spun the narrative for the common folk that it was merchants (price-setters) who were to blame for the war.
Needless to say, price being a function of supply and demand, and the post-zollvereini/unification interdependence of the German commodities economy was not as popularly-understood of a concept as antisemitism.
The reality was that the war was poorly-planned and poorly-executed, but this was an unconscionable admission for the Prussian elites.
This was one of the load-bearing columns for the dolchstoss myth that was weaponized to develop German anti-semitism in the interwar years.
In fairness, no country in a pact attacked another country in its pact. The issue was there were 2 competing and independent alliance groups rather than 1 (World) trade group.
Take something as simple as boots. In war, soldiers are usually doing a lot of walking and good boots prevent many injuries and improve effectivity of troops. So suddenly you decide to send millions of conscripts into war. Sadly you have outsourced the boots manufacturing industry to the country you are waging war with. Had the industry been in your country, you could have told them to retrofit their lines to manufacture your boots, but sadly all the knowledge, together with the population that is used to the repetitive nature of factory work is in a different country now.
Remember how much struggle there was distributing even simple things like masks and PPE during the COVID pandemic?
Of course you can solve the boots problem, but you'll have the same variant of problem for a lot of things. Solving all these problems all at once is an insurmountable task.
Even building a single Photolitography plant takes hundreds of millions of USD and years from start of planning to conclusion, with the involvement of a large number of companies from around the globe, each specialized to their own part of the process, and world leader in that part. So where will you manufacture your chips needed for your autonomous robot army?
