Claims over these regions turned violent in 1919 with a brief military conflict, the Seven-day war, between Polish and Czechoslovak units. The Allied governments pressed for a ceasefire and on 3 February 1919 a Polish–Czech border agreement was signed on the basis of the 5 November 1918 ethnic division agreement. This was later changed at the Conference of Ambassadors in Spa, Belgium on 28 July 1920. Cieszyn () was divided along the Olza river between the two newly created states of Poland and Czechoslovakia. The smaller western suburbs of Cieszyn were joined to Czechoslovakia as the new town of Český Těšín along with the railroad and the Karvina coal basin. Poland received the portion of Cieszyn east of the Olza river. The Conference of Ambassadors divided the region just as the Red Army was nearing Warsaw.