After the war ended, he belonged to several right-wing paramilitary groups, and fought in the Kapp Putsch, the Silesian Uprisings and against the French occupation of the Ruhr.

Upon the outbreak of the First World War, he joined the Imperial German Army on 1 August 1914 as a Fahnenjunker (military cadet) with the 4th (1st Silesian) Dragoon Regiment "von Bredow" in Lüben (today, Lubin).

[1] From 1919 to 1922 Finckenstein was a member of various Freikorps units, including the Freiwillige Sturmabteilung Schlichtingsheim and the Marinebrigade von Loewenfeld.

During this time, he took part in the suppression of the Third Silesian Uprising in Upper Silesia, and in fighting against the French occupation forces in the Ruhr.

On 20 June 1939, Finckenstein left his field command for a staff assignment with the Supreme SA Leadership (OSAF) in Munich, and he was promoted to SA-Obergruppenführer on 30 January 1941.

[6] He first joined the Nazi Party in June 1923, and rejoined it on 25 September 1925 (membership number 19,599) after it was refounded following the ban imposed after Adolf Hitler's unsuccessful Beer Hall Putsch.

He was assigned to Fusilier Regiment 68 and, in 1943, he was made a Major in the Landesschützen (State Riflemen) Reserve Battalion 4 in Glauchau.