Bloody Sunday, when 13 people were killed and about 60 wounded. Confirmed by the 1919 Treaty of Saint-Germain-en-Laye, the border between Yugoslav and Austrian Styria mostly followed the ethnic-linguistic dividing line between Slovenes and ethnic Germans. Nevertheless, several Slovene-speaking villages around Leutschach, Spielfeld, Soboth, and Bad Radkersburg remained in Austria. On the other hand, several predominantly German-speaking towns remained in Yugoslavia, especially Maribor (80% German speakers), Ptuj (86%), and Celje (67%); in addition, the German-speaking area around the village of Apače was annexed to Yugoslavia. According to the 1921 Yugoslav census, some 22,500 ethnic Germans lived in Yugoslav Styria. They represented around 4.5% of the overall population of the region, and around 57% of all ethnic Germans in Slovenia. In 1931, this number dropped to around 12,500 or 2.3% of the regional population, and around 45% of all ethnic Germans in Slovenia. In 1922, the County of Maribor was formed, comprising most of the territory of Slovene Styria, plus the Prekmurje and the Međimurje regions. After the coup d'etat of King Alexander I of Yugoslavia in January 1929, the counties were abolished and replaced with nine Banates (Slovene: Banovina). Following the reorganization implemented by the Yugoslav constitution of 1931, Slovene Styria was incorporated in the newly established Drava Banovina, which was more or less identical with Slovenia, with Ljubljana as its capital city. In April 1941, Nazi Germany invaded Yugoslavia and Slovene Styria was annexed to the Third Reich. A policy of violent Germanization was introduced. Public use of Slovene was prohibited, and all Slovene associations were dissolved. Members of all professional and intellectual groups, including many clergymen, were expelled. Between April 1941 and May 1942, around 80,000 Slovenes (almost 15% of the overall population) were expelled from Lower Styria, or resettled to other parts of the Reich. As a reaction, a resistance movement developed. Many areas of Lower Styria witnessed fierce fighting between German troops and Slovene partisan units. After World War II, Yugoslav authority over the region was established and Slovene Styria became an integral part of the Socialist Republic of Slovenia. According to prior decisions made by the Anti-Fascist Council of the People's Liberation of Yugoslavia, an expulsion of the remaining ethnic German population was carried out, regardless of their links to the Nazi regime. Between the 1950s and 1970s, many areas of the region underwent rapid industrialization. Towns like Maribor, Celje, and Velenje became among the