The most authoritative tally of history's most murderous regimes is in a book by University of Hawaii's Professor Rudolph J. Rummel, "Death by Government." Statistics are provided at his website. The Nazis murdered 20 million of their own people and those in nations they captured. Between 1917 and 1987, Stalin and his successors murdered, or were otherwise responsible for the deaths of, 62 million of their own people. Between 1949 and 1987, Mao Tsetung and his successors were responsible for the deaths of 76 million Chinese.
Today's leftists, socialists and progressives would bristle at the suggestion that their agenda differs little from Nazism. However, there's little or no distinction between Nazism and socialism. Even the word Nazi is short for National Socialist German Workers Party. The origins of the unspeakable horrors of Nazism, Stalinism and Maoism did not begin in the '20s, '30s and '40s. Those horrors were simply the end result of long evolution of ideas leading to consolidation of power in central government in the quest for "social justice." It was decent but misguided earlier generations of Germans, like many of today's Americans, who would have cringed at the thought of genocide, who built the Trojan horse for Hitler to take over.
Few Americans have the stomach or ruthlessness to do what is necessary to make their governmental wishes come true. They are willing to abandon constitutional principles and rule of law so that the nation's elite, who believe they are morally and intellectually superior to the rest of us, can have the tools to implement "social justice." Those tools are massive centralized government power. It just turns out last century's notables in acquiring powerful central government, in the name of social justice, were Hitler, Stalin, Mao, but the struggle for social justice isn't over yet, and other suitors of this dubious distinction are waiting in the wings.