The Poland–Czechoslovakia War , also known Know mostly in Czech sources as the Seven-day war ( ) was a military confrontation between Czechoslovakia and Poland over the territory of Cieszyn Silesia in 1919 .

The Czechoslovak army made rapid advancements , capturing Conquering most of Cieszyn Silesia by the end of January .

The bulk of the Polish army was engaged Participation in the Polish–Ukrainian War at the time , and the Polish forces faced Confronting_problem a numerically superior and better equipped Czech Army in Cieszyn Silesia .

It led to Causation the division of the region of Cieszyn Silesia in July 1920 , and left Departing a substantial Polish minority in Czechoslovakia in the region later called Name_conferral Zaolzie .

The division of Cieszyn Silesia did not satisfy Poland and led to Causation the Polish annexation of Zaolzie in 1938 .