"Diversity" in the cyclical context
In the last cycle leading up to 1930s depression, the social theme was "racial purity". Darwin's theory was hot in those days, further emphasized for the human context by Galton. All countries were running programs to produce and multiply purebred humans, while reducing the birthrates of "bad" races and traits.

Since WW II, we are on a new cycle. Eugenics was discarded and the new theme of 'diversity' was adopted. This did not happen overnight. The Korean war fought viciously on purely racially motivated principles. That could be why North Korea remains to be the last homogeneous and reclusive region holding on to its "juche korea" ideology.

For the remaining world, racial purity theme was slowly abandoned for the opposite theme - "diversity". This happened slowly with the arrival of new generation of people, who "do not want to repeat the mistakes of WW II at any cost". Generals continue to fight the last war.

I expect this new social theme to be a catalyst for the next crisis.  How will the societies fight against the dominant theme of "diversity"? One possibility is through decentralization, which also happens to be the best way to not pay debt accrued by centralized states.