During World War II on 16 June 1945, he was part of a group in Berlin that founded the Liberal Democratic Party of Germany (initially intending to re-use the name "Deutsche Demokratische Partei" of a Weimar-era party), becoming one of its board members. The LDP later became one of the bloc parties under the East German communist regime, after whose fall it merged in 1990 with the West German Freie Demokratische Partei (trans. "Free Democratic Party"), which is affiliated with ideology of classical liberalism. Kappus died on 9 October 1966 in Berlin, Germany at the age of 83.