6 June – July 1919 The Hungarian Red Army takes the cityMaďarská Červená armáda obsadzuje mesto

The new border had to be fought for. In the summer of 1919 the Hungarian Red Army — the army of the communist government in Budapest — pushed north into Slovakia and took Košice on 6 June 1919; ten days later a Slovak Soviet Republic was proclaimed at Prešov, an hour up the road. Under Allied pressure Budapest agreed to withdraw, and Czechoslovak troops were back in Košice by July. The border itself was confirmed by the Treaty of Trianon on 4 June 1920, which left Košice in Czechoslovakia and a large Hungarian-speaking population inside it. That unresolved argument about who the city belonged to would be reopened, by force, in 1938.O novú hranicu sa muselo bojovať. V lete 1919 postupovala Maďarská Červená armáda — vojsko komunistickej vlády v Budapešti — na sever do Slovenska a 6. júna 1919 obsadila Košice; o desať dní bola v Prešove, hodinu cesty odtiaľto, vyhlásená Slovenská republika rád. Pod tlakom dohodových mocností Budapešť súhlasila s ústupom a v júli boli v Košiciach opäť československé vojská. Hranicu potvrdila Trianonská mierová zmluva zo 4. júna 1920: Košice zostali v Československu a s nimi aj početné maďarsky hovoriace obyvateľstvo. Tento nedoriešený spor o to, komu mesto patrí, sa v roku 1938 otvoril znovu — a násilím.