China is a lot bigger market than the US. EU is slightly bigger. US is third. Maybe with extended markets (e.g. Central America and Canada for US, Eastern Europe for EU, Belt and Road area for China, US is number two). You need to consider several factors, like number of people, as well.

A big problem for the US is that it is a litle off, while most other social/cultural areas are closely connected. For instance, China and Russia might be almost as close allies as the pre-Trump US and Europe. But because Russia and Europe are so close, in fact the business dependencies between both are quite high as well. So a lot of business happens in that exchange, with high values due to the political risks. Since the US lacks such interdependencies with close neighbors it can survive better in a time like WW2 but it is harder in a long peace time like we currently have.