Slovene and German ethnic nationalism increased during the 19th and early 20th centuries. With the collapse of Austria-Hungary in 1918 as a result of World War I, Celje became part of the Kingdom of Serbs, Croats and Slovenes (later known as Yugoslavia). During this period, the town experienced a rapid industrialization and a substantial growth in population.
slovene and german ethnic nationalism increased during the 19th and early 20th centuries with the collapse of austria-hungary in 1918 as a result of world war i celje became part of the kingdom of serbs croats and slovenes (later known as yugoslavia) during this period the town experienced a rapid industrialization and a substantial growth in population