After the First World War, Schlieper continued to serve in the Weimar Republic's Reichswehr and when the Weimar Republic was replaced by Nazi Germany, he remained in the Heer component of the Wehrmacht and from 1935 to 1939 commanded the 17th Artillery Regiment. In 1939, he was promoted to Generalmajor and served as Chief of Staff for Military District XIII and during the Invasion of Poland, served as the Chief of Staff for Frontier Sector Center. From 1939 to 1940, he was also the Quartermaster for the 18th Army.