After the conclusion of the
Polish–Soviet War, Bortnowski traveled to Paris, France, where he began training at the
École Supérieure de Guerre on 1 November 1920. In September 1922, he graduated and returned to Poland where he received further training at various posts, notably in the staff of the Army Inspectorate in
Wilno (modern Vilnius, Lithuania). On 15 August 1924, he was promoted to the rank of
colonel and in October of the following year, he became the commanding officer of the
Kutno-based 37th Infantry Regiment. After the
May Coup d'État in 1926, he served as the Chief of the 3rd Branch of the General Army Staff for two months starting in November. In February 1928, he was appointed commander of the
26th Infantry Division in
Skierniewice. From June 1930, he was transferred to
Poznań where he was appointed commander of the
14th Infantry Division. In October 1930, was assigned to the Army Inspectorate in Toruń as an officer. On 1 November 1931, he took command of the
Zamość-based
3rd Legions Infantry Division, one of the most prestigious units of the Polish Army. On 1 January 1932, Bortnowski was promoted to the rank of
brigadier general by
President Ignacy Mościcki. Starting from 12 October 1935, he served as an Inspector General of the Armed Forces at Toruń. In the autumn of 1938, Bortnowski took command of the
Independent Operational Group Silesia which took participation in the occupation of Czechoslovak territory resulting from the
Munich Agreement. Specifically, Bortnowski's troops occupied the Czechoslovak territory of
Trans-Olza. The popularity of Bortnowski after his successful invasion and occupation of Trans-Olza was so great back in Poland, that he was planned to replace
Marshal Edward Rydz-Śmigły as commander-in-chief when the latter was to run for the presidency in the planned 1940 elections. Prior to the outbreak of the
September Campaign in September 1939, Bortnowski was promoted to the rank of
division general on 1 March 1939, and became the commanding officer of
Pomeranian Army, the northernmost of the
Polish armies to take part in the war. ==September Campaign==