Tresckow left the army after the war and pursued a career as a stockbroker. However, in 1924 he rejoined the army and by 1939 had reached the rank of lieutenant colonel and was serving on the staff of his uncle, Fedor von Bock, at AG Centre Headquarters.
In 1939 Tresckow was involved in the invasion of Czechoslovakia and Poland. He was appalled by the actions of the Schutz Staffeinel (SS) and the Gestapo in the occupied territories. After Tresckow witnessed the killings of captured soldiers in the Red Army in 1941 he decided that the government of Nazi Germany had to be overthrown.
In 1942 Tresckow became a general staff officer in the high command of the Army Group Centre. Over the next couple of years he used his access to senior army officers to try and recruit them join his conspiracy to overthrow the German government. Adolf Hitler. Fedor von Bock, Gunther von Kluge, Erich von Manstein and Gerd von Rundstedt all refused but were sympathetic enough not to inform the Gestapo about his activities.
On 14th March, 1943, Tresckow and his adjutant, Fabian Schlabrendorff, put a bomb on a plane carrying Hitler to Smolensk but the detonator malfunctioned and the bomb failed to explode. Tresckow still remained undetected and the following September was made chief of staff to the Second Army.
Tresckow had recruited Claus von Stauffenberg in 1942 and he was chosen to plant a bomb at a meeting attended by Hitler on 20th July, 1944. Stauffenberg carried the bomb in a briefcase and placed it on the floor while he left to make a phone-call. The bomb exploded killing four men in the hut. Hitler's right arm was badly injured but he survived the bomb blast.
The assassination must be attempted, at any cost. Even should that fail, the attempt to seize power in the capital must be undertaken. We must prove to the world and to future generations that the men of the German Resistance movement dared to take the decisive step and to hazard their lives upon it. Compared with this, nothing else matters.
I shall shoot myself. Probably only a few can imagine what fate would have befallen Germany if the plot had succeeded. I thank Providence and my Creator, but not because he has preserved me. My life is solely devoted to worry, to working for my people. I thank Him, rather, because He had made it possible for me to continue to shoulder these worries, and to pursue my work to the best of my abilities and according to my conscience.