Hi there, first post here so I apologize if I mess up with the etiquette! I was on Wikipedia (not always the most reliable, I know) looking at the list of World War I versus World War II casualties and I noticed that it listed the Austro-Hungarian Empire's WW1 population as 51.4 million, whereas in WW2 Austria had 6.6 million people and Hungary 9.1 million people. I'm aware that the Austro-Hungarian Empire then owned more territories, like Subcarpathia and their annexed parts of Poland (Wikipedia claims these parts of Poland were home to about 3,5 million people), but from what I understand those territories would not explain such a huge population loss, even with the Empire's WW1 casualties. I'd love to hear from someone who has an explanation for this!
Thank you for any responses!
The loss of territories after World War I will actually mostly explain this.
The population of Austria-Hungary in 1910 was (as noted) just over 51 million people. 28 Million lived in Cisleithania (ie, the Empire of Austria), and 20.8 million lived in Transleithania (ie, the Kingdom of Hungary). A further 2 million lived in Bosnia, which was an Austro-Hungarian condominium.
First, in Austria's case, the provinces that would (largely) make up postwar Austria only had about 7 million inhabitants in 1910: Upper Austria (800,000), Lower Austria (including Vienna for 3.2 million), Styria (1.4 million), Carinthia (400,000), Tyrol (900,000), Salzburg (200,000) and Vorarlberg (145,000). Even these territories had significant areas that were ceded by Austria after the war, notably in Tyrol (to Italy) and Styria (to Yugoslavia). Other provinces had much larger populations: Bohemia (6.7 million), Moravia (2.6 million) and Silesia (700,000) went to Czechoslovakia, while Galicia (8 million) went to Poland, Bukovina (800,000) to Romania, and Istria (1 million), Carniola (500,00) and Dalmatia (600,000) to Yugoslavia.
The Kingdom of Hungary was much more of a unitary state, so it's a bit harder to break down its 20.8 million, although 2.6 million of those inhabitants were in Croatia-Slavonia, which went to Yugoslavia. But otherwise, yes - Hungary lost almost 3/4 of its territory and more than half its population in the Treaty of Trianon, with some 5.3 million in territories annexed by Romania, 1.5 million in territories outside of Croatia-Slavonia that were also annexed by Yugoslavia, 291,000 in Burgenland (which was annexed by Austria), and 3.5 million in Upper Hungary-now-Slovakia, which was annexed by Czechoslovakia.
So while World War I casualties and general population movements would have played some role in diminishing Austria and Hungary's postwar population sizes, much of it did come from losing populous territories to other states in the postwar settlement. Almost 13.5 million of Austria-Hungary's 51 million (a quarter of the total) wound up in Czechoslovakia alone.
