Tonight's thread—as promised, is on concentration camp history leading up to WWII and the Holocaust. (Tuesday's thread was the first decade of camps. Wednesday was the rise of global internment in WWI.)
People tend to look for causal links in concentration camp history. But the WWI globalization of camps created detention systems all over the world. There was little need to directly mimic other camp systems once nations had their own bureaucracies to tap into or revive.
Concentration camps diversified as countries added their own cultural and penal twists to mass civilian detention. But the biggest change in the wake of WWI was that countries went from detaining enemy alien civilians in wartime to locking up their own citizens.
The same propaganda was used to strike fear into the heart of the larger population. The same vilification of targeted groups occurred. But by the 1920s, those designated terrorists, degenerates, or a threat to national security were fair game, even if they weren't foreigners.
After extracting Russia from WWI, the Bolsheviks began using camps against political enemies. Once they won the Civil War & founded the USSR, the idea of re-educating people through detention & labor took hold, leading to the formal creation of the Gulag at the end of the 1920s.
Across nearly three decades of the Gulag's existence, millions upon millions of people were detained as part of a larger terror strategy to shape society. Mass executions, regional starvation, spy networks, & tiny, daily threats to employment or education rounded out the toolkit.
It might be tempting to tie the rise of Nazi camps to the Gulag, as if the Soviet experiment inspired the horrors of German concentration camps. But it is not necessary to make that reach. Just like Russia, Germany had its own civilian detention camps during WWI.
Hitler spoke about wanting to put Jews in concentration camps as early as 1922. But he was thinking then of the most recent camps that had existed: the internment camps of WWI. The idea of Nazi camps began as something very different than the death factories of the Holocaust. 
I'm embedding a thread here that I did on Kristallnacht a few days ago, which talks about the evolution of Nazi camps. But in the mid-1930s, these camps were chiefly for political opponents, then vagrants, Roma and Sinti ("Gypsies"), and homosexuals.
One thing I found researching camp systems around the world is that there's often a pivotal moment 3 or 4 years in, an inflection point at which camps are either closed or their presence is more firmly established. Germany had that inflection point, too.
None of this is to say that the Nazis weren't responsible for all the evil they unleashed. They were & are. They chose to expand the camps. They deliberately made them more & more lethal. But at the start, even they didn't imagine camps at the heart of industrialized genocide.
Germany ended up with something different than any camp system in history then or since: the fully dedicated warping of a nation's policy, materiel, and technology to the eradication of a people. But we should not assume that such a thing can never happen again.
Tomorrow I'll talk about how, after WWII, the term "concentration camp" became associated only with death camps, breaking a critical link with the system those camps had risen out of. Meanwhile, under various names, sites of mass civilian detention flourished around the world.
