Upon leaving the service in 1918, Zaisser joined the Independent Social Democratic Party of Germany (USPD) and in 1919 returned to Essen, where he became a school teacher.

Starting in 1927, Zaisser worked almost exclusively for the Executive Committee of the Comintern, serving as a military advisor to China (1927–1930) and the Czechoslovak Army (1930–1932).

[3] Wilhelm Zaisser's deputy was a career NKVD operative and future Stasi Minister Erich Mielke, who used the cover name "Fritz Leissner."

Military advisors like Vladimir Antonov-Ovseenko, journalists like Koltsov were open to infection by the heresies, especially Trotsky's, prevalent among the Republic's supporters.

NKVD agents sent to Spain were therefore keener on abducting and murdering anti-Stalinists among Republican leaders and International Brigade commanders than on fighting Franco.

Following the end of the Spanish Civil War in 1939, Zaisser returned to Moscow to resume working for the Comintern, but was thrown into jail, apparently because of the failure of the Soviet intervention in Spain.

Alarmed by the uprising, Lavrenty Beria, the First Deputy Premier of the Soviet Union and head of the Ministry of Internal Affairs, personally travelled from Moscow to East Berlin.

[7] By the end of the meeting, only two Politburo members still supported Ulbricht's leadership: Free German Youth League chief Erich Honecker and Party Control Commission Chairman Hermann Matern.

Ulbricht only managed to forestall a decision then and there with a promise to make a statement at the forthcoming 15th SED CC Plenum, scheduled for later that month.

[7] Meanwhile, Mielke informed a Party commission looking for scapegoats that Zaisser, was calling for secret negotiations with West Germany and that, "he believed the Soviet Union would abandon the DDR.

"[8] Once he knew he had the complete support of new Soviet Premier Nikita Khrushchev, Ulbricht removed Zaisser and all other critics of his leadership from the SED's ruling Politburo.