So you get in a position where there is a kind of two-dimensional struggle: left-right/inside-outside. The Social Democrats were now ‘inside’, the new core of the so-called Weimar coalition that held power through the 20’s. The traditional, Wilhelmine conservative forces were still insiders, by any reasonable calculation. They had tremendous social and institutional leverage everywhere – not to mention most of the money – but they couldn’t compete electorally for a time. Some really strange stuff happened. Some of the most vicious in-fighting was on the left, especially between the social democrats and the communists, starting right in 1918.
From the balcony of the Reichstag building, the SPD leader Philipp Scheidemann proclaimed a German Republic. A couple of hundred meters away, from the balcony of the royal palace, the famed radical socialist and antiwar activist Karl Liebknecht proclaimed a socialist republic. Ebert [a social democrat who didn’t like the suddenness of it all] was furious. He discounted Liebknecht, recently released from the kaiser’s jails, as a wild radical who might just as well have languished longer in prison. But Scheidemann was his close colleague, and no recognized body, no government, not even a political party, had authorized the proclamation of a republic. There had not even been a discussion. (Eric D. Weitz, Weimar Germany: Promise and Tragedy, p. 19)
The Social Democrats where forever fighting with the communists, after that. So, on the one hand, the SD’s were solidifying a grand coalition with more centrist parties, proclaiming women’s rights, a free press, freedom of religion, an expanded welfare state; on the other hand, they were forced to use the proto-Nazi Freikorps to put down the Spartacist League, leading to the murders of Leibknecht and Rosa Luxemburg. Forced because they literally had no police/military alternative. Right-wing paramilitaries were the only available muscle. The SD’s had to work with the powers-that-still-were. Obviously the correct conclusion to draw is not that the SD’s were really right-wingers themselves – or that the Freikorps had left-wing sympathies. Each group tried to use the other. The SD’s wanted to save the Weimar Republic, by any means necessary. The Freikorps wanted to murder communists and gain the sort of legitimacy that might allow them, eventually, to overthrow the Republic – to whose existence they were not reconciled.-----------
Sort of like Cersei arming the Sparrows and bringing back the Faith Militant who turn on her.