He was a member of the SDP in 1918 and anti-war back when he was 17, he initially said the Bolsheviks were disorganized in 1925, but gave some praise to Lenin in 1929 as a defender of democracy.

He was saying some pretty radical shit all through the 30s and 40s about a global communist state and the abolition of capitalism (his stark radical turn spurred on by nuclear war clearly), and eventually the feds had an almost 1500 page file on him.

Seems like his tendency of socialism (at least earlier on) was Georgism, but "Why Socialism" diverts from that ideological current so there was definitely an evolution of ideas (and I believe an acceptance of the Soviet system as mostly good and practical)

There's a whole wiki on it

Edit: He was a Zionist, but definitely not a modern Zionist:

I should much rather see reasonable agreement with the Arabs on the basis of living together in peace than the creation of a Jewish state. My awareness of the essential nature of Judaism resists the idea of a Jewish state with borders, an army, and a measure of temporal power, no matter how modest. I am afraid of the inner damage Judaism will sustain—especially from the development of a narrow nationalism within our own ranks, against which we have already had to fight strongly, even without a Jewish state. ... If external necessity should after all compel us to assume this burden, let us bear it with tact and patience.

I think this was actually a pretty common position among a lot of leftists at the time too, even Stalin initially supported Israel which when formed has a pretty large socialist/communist bloc. I do wonder if a less militarized and colonial formation of a Jewish homeland could have been pulled off or if it was always destined for nationalism and violent rot.

I feel that the conditions that led to Israel as it is today have a lot to do with the colonial empires (USA/UK) that had such a hand in establishing, funding, and shaping it.