“We are on the field of battle. The audience in the hall is divided in two sections: it is as if a knife has cut them sharply in two. Two parties are present.” Grigory Zinoviev’s description of the Halle congress of the Independent Social Democrats (USPD) in October 1920. Would the USDP and its 700,000 members opt for the Third International or attempt to stay a halfway house floating uneasily between communism and official social democracy? The Halle congress would decide.