From the 1930s to the 1960s, the Bronx was known for its tranquility, with children playing outside unaccompanied, bikes and scooters left unattended, and doors left ajar for fresh air (!). 
The author, Carl Hansen, moved from Omaha, Nebraska to DC to join the public school system there. He was shocked and horrified by segregation in DC, which he regarded as evil, and made up his mind to do all he could to oppose it. 
I'm sure everyone who follows me has seen the "Britain immigration charts" a few times, but I'll post them again here. Severe 21st century economic dysfunction, declining physical capital stock per person. 
Apropos of nothing: immigration lowers national IQ almost everywhere. 
The multiethnic nature of Austria-Hungary meant that it could not separate domestic and foreign policy; every foreign issue had a domestic lobby and vice-versa. 
I think race (and ethnicity/LGBT - Mamdani's white support is probably ~50% Jewish and very gay) are much more salient to why Millennial socialism is a major political force than downwards mobility among elite. 
Unconditional surrender was publicly adopted as a war goal in Jan 1943, with the idea of preventing WWIII, as many Germans, including Hitler, thought Germany had not been beaten militarily in WWI and as such wanted to fight WWII. This caused trouble later. 
The genesis of the simultaneous Japanese attacks on Midway and the Aleutians Islands: the IJN had won so hard so fast (Pearl Harbor, Malaya/Singapore, Indian Ocean raid, Philippines, Dutch East Indies), they didn't have any obvious next thing to do. 
First thing to understand about the Raj is that it was practically an empire of its own within the British one, and with a great of autonomy though not self-government. India was a signatory of the Treaty of Versailles. 30M Indians emigrated to other parts of the Empire. 
3/4 of this tiny population (outnumbered by more than twice as many Indians, because Mexico did not actually control this territory, hence inviting Anglo settlers) was in New Mexico.
South African GDP grew at 8.3% per year from 1945-65 (admittedly, with extremely high black population growth). 
The map as of the end of WWII. Communists had very strong influence in northern China, not much in southern China or Manchuria. 
Given sharply limited resources, the Allied occupation authorities did not starve Germany, but did put it behind the rest of Europe on the priority list, for obvious reasons.
This is also why, even from a disembodied abstract "civilizationist" perspective, the common cope that Western civilization can be dragged into the mud but it will be OK because East Asia will keep the torch alive is wrong. 
Apollo and the Manhattan Project both happened while the United States was the most closed to immigration it had ever been in history. 
The Chinese see multiculturalism as a sickness in the American body politic destroying a formerly-strong principally Anglo-Protestant US society. Racism keeps Chinese society strong and united against outsiders. 
Germany, Japan, US, and UK all dedicated 65-80% of their economies to aircraft, ships, and anti-aircraft equipment. Aluminum, crtitical for aircraft production, was thus as or more important than the more famous (Rise and Fall of the Great Powers) steel production. 
By the way, since we know contraception/family planning/abortion were not in common use until 1760 (France)/1870 (rest of Europe) and bastardry/cuckoldry rates were both very low, we can be confident this goes back to at least 1300 (less evidence before then). 
