Too much concentration of wealth and assets and way too much indebtedness. Consumer spending is maxed out in the US. A thought experiment: If you own the world, what would you want to do? Solar energy for those who have nothing to give you in return or space exploration or something else you fancy? This had happened before in the US around 1929. There are some old federal reserve documents that describe exactly this situation. War, inflation, devaluation, and redistribution was the way out.

This is definitely a bigger problem in EU. Greece and Italy are top of the list with this problem and could benefit from a devaluation.