Hitler never trusted the professional army officers. His disdain came about because of the poor generalship in World War I that killed millions of German soldiers. He was always worried that the Army would attempt a coup de état and try to take over the government.
In 1934, as a result of the Night of Long Knives, he removed the SA, essentially a gang of thugs that had brought him to power, and killed their leader, Ernst Röhm. In exchange for removing the SA, the Army signed an oath of allegiance to Hitler.
As the losses mounted in late 1943 and early 1944, Hitler replaced or forced many generals into retirement and the Army high Command, except for those officers in Hitler’s personal orbit, grew openly critical of his constant meddling.
Oberst Claus Schenk, Count von Stauffenberg lost his left hand and fingers from his right fighting in Tunisia. As a member of the aristocracy, he had double contempt for Hitler, and joined the plot to kill him. General Ludwig Beck, Chief of Staff back in 1938, was the nominal leader.
The Normandy Landings inspired the plotters to attempt an assassination in the face of the Allied breakout. Von Stauffenberg placed a briefcase with a bomb inside Hitler’s “Wolf’s Lair” — his command post for the Eastern Front in Rastenburg, Prussia. The bomb was one of many British bombs confiscated by the Abwehr, the German intelligence organization. Stauffenberg had to activate the bomb with tongs. He placed the bomb under the conference table and left. He and the other plotters believed Hitler was dead and prepared to seize Berlin with Home Army troops.
Hitler was not dead. Believing God had spared him to avenge Germany on the world, he met with Mussolini later in the day despite wounds to his right arm and a loss of hearing.
Meanwhile, Stauffenberg was shot at midnight by a firing squad, loyal Army officers rounded up conspirators, many of whom tried to spare their lives by informing. Implicated was Erwin Rommel, who had been approached by the plotters but did not join. Rommel was recovering from wounds at home. For his failure to inform Hitler, he was given a choice: take poison and get a state funeral, or refuse and see your family executed as well. Rommel took poison. The man who had the best ability to change Germany’s fortunes of war was gone.