Below is a map that locates the main events that affected Hitler and Nazism.

Martin Heidegger and his controversy.
Martin Heidegger (1889-1976), author of Being and Time (1927), is one of the most influential philosophers of the past century, however there is a controversy regarding his choice to remain in Germany while the majority of his colleagues emigrated to the USA or to other countries because they were Jews, or persecuted by Nazis for their ideas.
How could a man like Heidegger accept Nazism? He answered that he believed, like many others, that Hitler and Nazism would have started a new phase for Germany. Besides, Nazism appeared to him the only protection of the Da-sein (existence) from the Communist menace.
Thus Heidegger joined Nazism because he thought it would have protected the community, the projects and the language of Germany. However, after the war Heidegger, retracing his steps, defined Nazism as the expression of the Nihilism of the world-wide technical civilisation that made nothing.

Hannah Arendt and the Banality...

Below is a map containing a survey of the events that affected the 4 philosophers.

Genocide of the Armenians (Medz Yeghern, “Great Crime”)
The Young Turks (nationalist officers of the Ottoman Empire) ordered massive massacres against the Armenian Christian population between 1915 and 1923. Subsequent mass deportations will bring the number of victims to about one and a half million.

Genocide of the peoples of China 
In the year 1900, the Boxer Revolt caused over 30,000 deaths, mostly Christians, in Northern China. And at least 48 million Chinese have fallen under the Mao regime between the Great Leap Forward, the purges, the cultural revolution and the forced labor camps, from 1949 to 1975.

Genocide of the peoples in Russia 
No less than 20 million Russians were...