Hitler purged the SA’s militarist faction to keep the movement ideological

Evidence

Despite these militaristic trappings, the inner-party faction of the Nazis, which was primarily nationalistic and militaristic and therefore viewed the paramilitary troops not as mere party formations but as an illegal enlargement of the Reichswehr (which had been limited by the terms of the Versailles Peace Treaty), was the first to be liquidated. Rohm, the leader of the SA stormtroopers, had indeed dreamed of and negotiated for incorporation of his SA into the Reichswehr after the Nazis seized power. He was killed by Hitler because he tried to transform the new Nazi regime into a military dictatorship. Hitler had made it clear several years before that such a development was not desired by the Nazi movement when he dismissed Rohm—a real soldier whose experience in the war and in the organization of the Black Reichswehr would have made him indispensable to a serious military training program—from his position as chief of the SA and chose Himmler, a man without the slightest knowledge of military matters, as reorganizer of the SS. — Hannah Arendt, The Origins of Totalitarianism, 861

Categorization

• XREF: Hitler choosing the militarily ignorant Himmler over the competent soldier Rohm anticipates the totalitarian preference for ideological loyalty over technical competence that pervades Arendt’s account.