“The Socialists, and I am still one, although an exasperated one, never brought forward the question of irredentism, but left it to the Republicans. We are in favour of a national war. But there are also reasons, purely socialist in character, which spur us on towards intervention.”

No Compromise – No Political Trading (1899)
Context: The internationality of socialism is a fact that is daily becoming more evident and more significant. We socialists are one nation to ourselves, – one and the same international nation in all the lands of the earth. And the capitalists with their agents, instruments and dupes are likewise an international nation, so that we can truthfully say, there are to-day only two great nations in all lands that battle with each other in the great class struggle, which is the new revolution – a class struggle on one side of which stands the proletariat, representing socialism, and on the other the bourgeoisie, representing capitalism. While the bourgeois world of capitalism continues and the bourgeoisie rules, so long are all states necessarily class states, and all governments class governments, serving the purposes and interests of the ruling class, and destined to lead the class struggle for the bourgeoisie against the proletariat – for capitalism against socialism, for our enemies and against us. From the standpoint of the class struggle which is the foundation of militant socialism, that is a truth which has been raised by the logic of thought and of facts beyond the possibility of a doubt. A socialist who goes into a bourgeois government, either goes over to the enemy or else puts himself in the power of the enemy. In any case the socialist who becomes a member of a bourgeois government separates himself from us, the militant socialists. He may claim to be a socialist but he is no longer such. He may be convinced of his own sincerity, but in that case he has not comprehended the nature of the class struggle – does not understand that the class struggle is the basis of socialism.

Source: Disputed, Hitler: Memoirs of a Confidant (1978), p. 26

As quoted in The Myth of the Nation and the Vision of Revolution: The Origins of Ideological Polarization in the 20th Century, Jacob Talmon, University of California Press (1981) p. 487
Undated

Speech in Berlin, April 7, 1938. Quoted in "The Trial of the Germans" - by Eugene Davidson - History - 1997

As quoted in The Ideology of Fascism: The Rationale of Totalitarianism, A. James Gregor, New York and London, The Free Press (1969) p. 106
Undated

Socialist newspaper Folkets Dagblad - Politiken (24 April 1918)

Source: The Ideology of Fascism: The Rationale of Totalitarianism, (1969), p. 141

Reagan biographer Lou Cannon noted that this was a suspect quotation, and that he could find no evidence of it. Thomas did say that both major political parties had borrowed items from the Socialist Party platform.
Cannon, Lou. Governor Reagan: His Rise to Power. New York: PublicAffairs Books, 2003. ISBN 1-586-48030-8 (p. 125).
Possibly Misattributed

As quoted in The New York Times (18 June 1950); also in Thomas Mann: A Critical Study (1971) by R. J. Hollingdale, Ch. 2