> The figures tended to be better when societies are more level, rather than simply richer.

Granting that this is true (and it's interesting if it is), what can or should be done?

If I wanted to make my society of 300,000,000 more "level," as Pickett & Wilkinson put it, how would I go about it?

"Tend" means that it some cases benefits don't accrue in spite of leveling. And when they do, what sort of effort and conditions bring the improvement about?