Career
Barth started his political career with the National Liberal Party. To that end, he sought the cooperation of the Social Democrats, and at multiple times voted against his own party. In the German Freeminded Party (Freisinnige Partei), founded in 1884, Barth would soon find himself opposed to the leadership of Eugen Richter.
In 1903, Friedrich Naumann would join the Freeminded Union as well.
Barth however would found the Democratic Union (Demokratische Vereinigung) in 1908, together with Rudolf Breitscheid and Hellmut von Gerlach, after the Freeminded Union"s participation in the Bülow-Block coalition in the 1907 elections. Barth founded the liberal weekly Die Nation (The Nation) in 1883 and remained as editor until his death in 1909.