Quoting Detlev Vagts’s Carl Schmitt’s Ultimate Emergency: The Night of the Long Knives:

A little more than a year into his rule as [Fascist] Chancellor, Hitler felt threatened from two directions. On the one hand there was restiveness among members of the SA (Sturmabteilung), the brown‐shirted street fighters who had done so much to bring him to power. Some of them took seriously the idea that there was meaning to the words “socialist” and “workers” in the title of the National Socialist German Workers’ Party. They felt that their contributions had not been recognized or rewarded.

Their head, Ernst Röhm, was a formidable fighter and potential troublemaker. He was intent upon gaining primacy in military matters vis‐à‐vis the army. On the other side, there was unease among the conservatives who had opened the way for Hitler’s appointment. Several of them were planning to meet with President Hindenburg to urge him to curb what they regarded as excesses in Hitler’s policies. Most disturbingly of all, the army leadership was considering forceful means to end the attempt by the SA to gain control over military matters[.]

It seems likely that subjectively Hitler took these threats seriously, though no evidence of any plot to seize power was ever presented. Witnesses describe him as highly excited to the point of foaming at the mouth. He flew to Munich and there confronted leaders of the SA in a resort hotel and had them imprisoned. One of Röhm’s chief deputies was caught in bed with another man, a matter that Hitler stressed in moralistic terms. Röhm was seized and given a chance to commit suicide; when he declined he was shot to death by SS (Schutzstaffel) officers.

Elsewhere in [the Third Reich] murder squads went into action. They killed General Kurt von Schleicher, Hitler’s immediate predecessor as Chancellor, together with his wife and an aide, General Bredow. Also on the list were Edgar Jung, secretary to Chancellor von Papen, who had drafted a critical article about Hitler’s excesses, and Erich Klausener, head of the Catholic Action movement. Schmitt had interacted with von Schleicher in various ways.⁵

Hitler also settled scores with men who had incurred his displeasure along the way: Gregor Strasser, formerly an important Nazi organizer, and Gustav von Kahr, a figure in Bavarian politics in the 1920s. Hitler’s enemies on the left were spared as they were already stowed away in concentration camps.

Some were killed by mistake, confused with a target having a similar name. No list of the assassinated was ever made public and the relevant files were destroyed. Hitler told the Reichstag that the number was 77; subsequent research indicates that the real number was twice or even three times as great.⁶

On July 13 Hitler spoke in the Reichstag to the German people, justifying his actions, and a statute was passed ratifying them. By and large the popular reaction in [the Third Reich] seems to have been favorable. Many regarded the SA as uncouth rowdies that constituted a menace to the public peace and the killings of the rightists were largely ignored, even by their comrades in the army. Only one officer dared to attend von Schleicher’s funeral.

Further reading: The Rise and Fall of the Third Reich, pages 213–226

Night of the Long Knives: Forty‐Eight Hours that Changed the History of the World

The Night of the Long Knives: The History and Legacy of Adolf Hitler’s Notorious Purge of the SA

Night of the Long Knives: Hitler’s Excision of Rohm’s SA Brownshirts, 30 June – 2 July 1934