There’s been some talk lately about US dependence on Taiwanese semiconductors or Chinese rare earth metals which could be interrupted if things go bad. An interesting question is to ask how many countries could fight a modern war in the face of total trade isolation.

Could say, once mighty Germany? 1/4th of Germany’s World War II gasoline was produced synthetically, another 1/4th just from Ploesti. If the entire army had to be mechanized (no horses) competition with the US or USSR would have been impossible even then (c. 1950).

World War II can be conceptualized in grand historical terms as the last stand of the medium sized country. Germany and Japan started wars with traditional enemies, only to discover that the demands of modern armaments required more invasions until self-sufficiency was reached.

When Albert Speer become Hitler's armaments chief he learned that Germany's war effort was critically dependent on the import of obscure natural resources. Speer believed the weakest link was chromium ore: under no circumstances could Germany have continued past January 1946:

During the war every leader became an industrial chemistry expert: Hitler insisted on fighting desperate battles for Nikopol and Lapland in order to secure supplies of magnesium; the British made a serious play to buy up all of Spain’s tungsten ore: https://en.wikipedia.org/wiki/Wolfram_Crisis

Germany’s resource demands were much lower in WWI, the primary problem being acquiring enough nitrate to both crops and produce explosives. Had Fritz Haber not solved the problem on the eve of war Germany would have needed to sue for peace at the end of 1914.

I’ve never heard this stated explicitly, but in retrospect Germany’s desperate dash through Belgium must have been predicated on this resource constraint. By 1914 though the problem was gone, meaning they would been much better off playing nice and keeping Britain out of the war