Key difference over tyranny is that totalitarianism is necessarily an expansionist movement with global aspirations, whose enemy is any truth or belief that could enable people to find a basis for agreement against it. It's total dominion of the human spirit through terror, where traditional 'isms are just nationally focused. When you break people with the randomness of the terror, they will oppress themselves.

In this model, North Korea is still just a national tyranny, and even China's CCP is a national police state with colonial aspirations, but it hasn't metastasized into a transnational movement. Hitlerism and Stalinism were the result of movements that created totalitarian empires. Arendt's view was it was a new form of government that was an artifact of the 20th century.