The decline - as documented in "The Spirit Level"
is a fairly specific fault that is more obvious in english-speaking advanced industrial countries than in Europe
Thomas Pekitty - in "Capital in the 21st Century"
spelt out what's going on - after having done a lot of work to document it - and the Spirit Level demonstrates that it's a bad idea.
Trump and Brexit are among the more florid symptoms, but there are plenty of others.
The aspects of the west captured by Scandinavia, Germany and the Netherlands illustrate the fact that the American and the British could do better (and probably would if they weren't so addicted to the idea that they are the ant's pajamas).
And Australia has a lot of the same problems - inequality isn't as bad here, but it is getting worse, and the local politicians couldn't care less.