After the 30 September 1938 Munich Agreement (which fatally wounded Czechoslovakia and, after the proclamation of the First Slovak Republic, led to the remainder of the country being taken over by Germany), Poland and Hungary worked through diplomatic and paramilitary means to restore their common border by engineering the return of Carpathian Ruthenia to Hungary.
In the aftermath of the 30 September 1938 Munich Agreement (which catastrophically affected Czechoslovakia and, following the creation of the First Slovak Republic, led to Germany's takeover of the rest of the country), Poland and Hungary cooperated through diplomatic and military means to re-establish their common border by arranging for the return of Carpathian Ruthenia to Hungary.