From From Peoples into Nations: A History of Eastern Europe, by John Connelly (Princeton University Press, 2020), Kindle pp. 463-464:
By 1941, three zones of influence had emerged in Nazi-dominated East Central Europe. The first included areas where Germany destroyed states and left no native administration, itself taking rudimentary control. The second comprised areas where it destroyed states and replaced them with its own political entities, misleadingly called “independent states.” In the third zone, states remained under control of native political elites, but they came under irresistible pressure to become German allies. Only Poland belonged to the first category.
The Protectorate of Bohemia and Moravia fit between the first and second zones: it was occupied and destined for absorption into Germany but valued as a place that produced high-quality industrial goods. Its population was thought to be racially valuable (50 percent of the Czechs were considered assimilable; only 10 percent of the Poles) and was permitted its own heavily supervised government, with a Czech cabinet and ministries, and even a tiny armed force. Serbia was similar, a rump, embodying nothing a Serb nationalist could be proud of, with a Serb head of state who had been a Royal Yugoslav general but was under direct Nazi oversight. As we have seen, in contrast to Bohemia, a desperate underground struggle raged, extending from Serbia across Yugoslav territory, pitting German, Italian, and Croat forces against Serb nationalists and Communist internationalists.
The second zone was made up of the “independent” states of Slovakia and Croatia, called into life by Berlin with the expectation they would be loyal, co-fascist regimes; and they matched expectations, to say the least. Their ultranationalist leaders were eager to demonstrate—above all to themselves—their personal achievements for “the nation” by becoming even more racist than the state that had created them. In 1941, a Slovak newspaper boasted that the strictest racial laws in Europe were Slovak; at the same time, the brutality of the Ustasha anti-Serb actions shocked even the SS.
The final zone consisted of states that technically remained sovereign members of the international community, yet whose leaders could see from the fate of Yugoslavia and Poland the consequences of defiance. Still, unlike the puppets Croatia or Slovakia, the Hungarian, Bulgarian, and Romanian states did not owe their existence to Nazi Germany, and everything Germany wanted from them had to be negotiated. The lever for Germany in gaining compliance was territory: though less rapacious than Nazi leaders, East European elites also hungered for Lebensraum. Bulgaria hoped to recover ground lost at Neuilly-sur-Seine and wrench away disputed lands from Greece and Yugoslavia. Hungary wanted back everything it had lost at Trianon. Romania desired the return of lands it had lost in 1940, when parts of northern Transylvania went to Hungary in the second Vienna award (at the insistence of Hitler and Mussolini), and Bessarabia and Bukovina fell to the Soviet Union. These three states knew that Germany as the regional hegemon could make their aspirations become a reality.
Yet from 1941, German diplomats increasingly insisted that the governments of East Central Europe must fulfill a prime wish of their state. They should identify and segregate their Jewish populations, place them under racial laws, and deport them to German-controlled territories in Poland for a fate loosely described as “work in the east.”