People of German nationality inhabited Croatian region of Slavonia (Slavonija) since 18th century.
After the region was depopulated due to decades of warefare and threats of war between Austro-Hungarian Monarchy and Ottoman Empire, Habsburg authorities made the land available to people from other parts of the monarchy for colonisation. Thus migrations to Slavonia became part of what is in the history known as Danube-Swabian migration.
By 1931, in about 100 settlements in Slavonia there were about 20 thousand inhabitants of Germanic origin. The largest German community was in Osijek (Esseg), with a little less than 10 thousand souls.
Other settlements with larger German population were Virovitica (German: Wirowititz; 2559 inhabitants), Retfala (Rietdorf; 1940), Đakovo (Diakowar; 1597), Gorjani (1376), Krndija (Kerndia; 1345), Slavonski Brod (Slawonisch Brod; 1167), Sarvaš (Sarwasch; 1157), Viškovci (1114), Vrbica (Wrbitza; 1025), Uljanik (972), Našice (Naschitz; 948), Tenja (Tenje; 877), Ernestinovo (Ernestinenhof; 838), Jovanovac (Johannesdorf; 792), Hrastovac (Eichendorf; 740), Spišić Bukovica (734), Petrijevci (Petrowitz; 733), Gašinci (Gaschinzi; 716), Tomašanci (Tomaschanzi; 643), Čačinci (Cainci; 635), Kula (also Josefsfeld; 600) Drenjski Slatnik (576), Mrzović (Merschovitz; 575), Miokovićevo (568), Kešinci (Keschinzi; 563), Semeljci (Semelzi; 562), Josipovac (Josefsdorf; 539), Antunovac (Antunowatz; 538), Našička Breznica (Deutsch Bresnitz; 532).
Although not in Slavonia, Croatian city capital Zagreb (in German language called Agram) also had a considerable German population of more than six thousand.
After the Second World War, many members of these communities migrated to Germany, so today in Croatia there is only a tiny minority of people with German origin.
More information about Germans from Slavonia can be found here.
Image: Drazenvk, Wikimedia Commons