He had joined the Social Democratic Party in 1911, but like hundreds of thousands of others he was radicalised by the evils of war, and during March 1919 would switch to the recently formed Communist Party. When revolution broke out in November 1918 he participated actively, joining Kurt Eisner in Bavaria, and turning up in Berlin shortly afterwards as legation secretary from the short-lived Bavarian Soviet (revolutionary government). He teamed up with Alfons Goldschmidt to help launch the "Räte-Zeitung", a four-page newspaper of the revolutionary "Workers' council" movement. He was a contributing editor to "Die Republik", a daily newspaper directed by the polymath anti-militarist Wilhelm Herzog. In Berlin during the first part of 1920 Dengel participated in defeating the Kapp Putsch and briefly became a member of the extremist breakaway Communist Workers' Party. Between September and December 1920 he visited Moscow. According to at least one source it was only after a visit to Moscow and a meeting with Lenin himself that during the first part of 1921 he returned to the mainstream Communist Party.