A better comprehension of how the borders have changed over time will help you understand migration patterns and can assist in determining the ethnicity of your ancestors.
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Other interesting history videos to help you understand how borders have changed.
The following is a summery of some historic regions in Europe, especially in the former Austro-Hungarian Empire:
The Banat is a geographical and historical region in Central Europe that is currently divided among three countries: the eastern part lies in western Romania (the counties of Timiș, Caraș-Severin, Arad south of the Körös/Criș river, and the western part of Mehedinți); the western part in northeastern Serbia (mostly included in Vojvodina, except a part included in the Belgrade Region); and a small northern part lies within southeastern Hungary (Csongrád county).
The region of Banat is populated by ethnic Romanians, Serbs, Hungarians, Germans, Krashovani, Ukrainians, Slovaks, Bulgarians, Czechs, Croats, Jews, Romani and other ethnicities.
Bačka (Serbian: Бачка / Bačka; Hungarian: Bácska, is a geographical and historical area within the Pannonian Plain bordered by the river Danube to the west and south, and by the river Tisza to the east. It is divided between Serbia and Hungary. Most of the area is located within the Vojvodina region in Serbia and Novi Sad, the capital of Vojvodina, lies on the border between Bačka and Syrmia. The smaller northern part of the geographical area is located within Bács-Kiskun County, in Hungary.
Bohemia (Czech: Čechy; German: Böhmen; Polish: Czechy; French: Bohême; Latin: Bohemia; Italian: Boemia) is the westernmost and largest historical region of the Czech lands in the present-day Czech Republic.
Bukovina (Romanian: Bucovina; German: Buchenland; Polish: Bukowina; Hungarian: Bukovina, Ukrainian: Буковина Bukovyna) is a historical region in Eastern Europe, divided between Romania and Ukraine, located on the northern slopes of the central Eastern Carpathians and the adjoining plains.
Galicia (Ukrainian and Rusyn: Галичина, Halyčyna; Polish: Galicja; Czech and Slovak: Halič; German: Galizien; Hungarian: Galícia/Kaliz/Gácsország/Halics; Romanian: Galiția/Halici; Russian: Галиция, Galicija; Yiddish: גאַליציע, Galitsiye) is a historical and geographic region in Central-Eastern Europe, once a small Kingdom of Galicia–Volhynia and later a crown land of Austria-Hungary, the Kingdom of Galicia and Lodomeria, that straddled the modern-day border between Poland and Ukraine.
Moravia (Czech: Morava; German: Mähren; Polish: Morawy; Latin: Moravia) is a historical country in the Czech Republic (forming its eastern part) and one of the historical Czech lands, together with Bohemia and Czech Silesia.
Silesia (Polish: Śląsk; Czech: Slezsko; German: Schlesien; Silesian German: Schläsing; Silesian: Ślůnsk; Lower Sorbian: Šlazyńska; Upper Sorbian: Šleska; Latin: Silesia) is a region of Central Europe located mostly in Poland, with small parts in the Czech Republic and Germany. Silesia is located along the Oder River. It consists of Lower Silesia and Upper Silesia.
Vojvodina (Serbian Cyrillic: Војводина), is an autonomous province of Serbia, located in the northern part of the country, in the Pannonian Plain.
YugoslaviaGenWeb (currently not accessible); Wikipedia: Yugoslavia
See: Serbia, Croatia, Slovenia, Macedonia, Montenegro, Bosnia-Herzegovina