Isaac Deutscher, born on this day in 1907, was a Marxist author and activist who played an important role in the British New Left after being expelled from the Polish Communist Party (KPP) for "exaggerating the danger of Nazism" in 1932. Deutscher is perhaps best known as a biographer of Leon Trotsky and Joseph Stalin.

Deutscher was born to a Jewish family in Chrzanów, in modern day southern Poland, then part of the Austro-Hungarian Empire. He first came to prominence as a poet, publishing verse in both Yiddish and Polish, concerned Jewish and Polish mysticism, history and mythology.

Around 1927, Deutscher joined the outlawed Polish Communist Party and very soon became the chief editor of the clandestine and semi-clandestine communist press.

Deutscher co-founded the first anti-Stalin group in the KPP, protesting the party view that social democrats were "social fascists". In an article "The Danger of Barbarism over Europe", Deutscher urged the formation of a united front against Nazism.

Deutscher was expelled from the Party in 1932, officially for "exaggerating the danger of Nazism and spreading panic in the communist ranks." The Nazis would invade Poland on September 1st, 1939.

Isaac had left Poland for London in April earlier that year to serve as a correspondent for a Polish-Jewish paper. After war broke out, he joined the Polish Army in Scotland, but most of his time in the Army was spent in the punitive camps as a "dangerous and subversive element" for protesting against institutional anti-Semitism.

In 1949, Deutscher published his first major work, "Stalin, A Political Biography". Following this, Isaac published his magnum opus, a three-volume biography of Leon Trotsky: "The Prophet Armed" (1954), "The Prophet Unarmed" (1959) and "The Prophet Outcast" (1963).

"Socialism does not aim at the perpetuation of the national state; its aim is international society. It is based not on national self-centredness and self-sufficiency, but on international division of labour and on cooperation. This almost forgotten truth is the very ABC of Marxism."

- Isaac Deutscher, in a 1958 interview with KS Karol, linked below