The recently created Slovak Republic joined the attack, and Field Army Bernolák contributed over 50,000 soldiers in three divisions.

[1][2] Since most of the Polish forces were engaged with the German armies, which were more to the north of the southern border, the Slovak invasion met only weak resistance and suffered minimal losses.

The official political pretext for the Slovak participation in the Polish Campaign was a small disputed area on the Poland–Slovakia border.

On August 26, Slovakia mobilised its armed forces and established a new field army, codenamed "Bernolák", with 51,306 soldiers.

The Bernolák army group was led by Slovak Defence Minister Ferdinand Čatloš and had its initial headquarters in Spišská Nová Ves, though after September 8 this was moved to Solivar near Prešov.

They were opposed by the Polish Carpathian Army, which consisted mainly of infantry units with some light artillery support and no tanks.

Two or three Slovak air squadrons (codenamed Ľalia, Lily) were used for reconnaissance, bombing and close support for German fighters.