In January 1919, the Polish–Czechoslovak War between Poland and Czechoslovakia began over the Duchy of Teschen. The Teschen region, which had a Polish majority and a Czech minority, was very rich in coal. However, the main reason that Kramář gave the Poles an ultimatum, demanding their withdrawal from Teschen, was to strengthen the Czechoslovak claim on the Sudetenland. To allow Teschen to join Poland because it had a Polish majority would create a precedent for the German-speaking Sudetenland to join Germany. Like other Czech politicians, Kramář insisted on the indivisibility of the former Austrian crownlands of Bohemia, Moravia and Silesia, arguing that everything that was once part of the Austrian Empire's "Czech lands" was now part of Czechoslovakia, and maintaining the claim on the Sudetenland that led Kramář to insist so forcefully that Teschen was part of Czechoslovakia.