In 1921, during the Silesian Uprisings, when Poland tried to separate Upper Silesia from the Weimar Republic, Strachwitz served under the Generals Bernhard von Hülsen and Karl Höfer. At the peak of the conflict when the Poles dug in on the Annaberg, a hill near the village of Annaberg—present-day Góra Świętej Anny. The German "Freikorps" launched the assault in what would become the Battle of Annaberg, which was fought between 21 May and 26 May 1921. Strachwitz and his two battalions outflanked the Polish positions and overran part of them in hand-to-hand combat around midnight on 21 May. Strachwitz was the first German to reach the summit. They captured six field guns, numerous machine guns, rifles and ammunition. On 4 June the "Freikorps" attacked Polish positions at Kandrzin—present-day Kędzierzyn—and Slawentzitz—present-day Sławięcice. In this battle Strachwitz and his men captured a Polish artillery battery which they turned against the Poles. For these services he received the "Schlesischer Adler" (Silesian Eagle) medal, Second and First Class with Oak Leaves and Swords. His younger brother Manfred also fought for Silesia, and was severely wounded leading his men at Krizova. Two months later his wife gave birth to their second child, a daughter named Alexandrine Aloysia Maria Elisabeth Therese born on 30 July 1921, nicknamed "Lisalex". The Ministry of the Reichswehr informed him in 1921 that he had been promoted to "Oberleutnant" (first lieutenant), the promotion backdated to 1916. The Strachwitz family grew further when on 22 March 1925 a third child, a son named Hubertus Arthur, nicknamed "Harti", was born on their manor at Schedlitz, later renamed Alt Siedel—present-day Siedlec.