Just as invasion is the true and tried weapon in the hands of capital against the class struggle, so on the other hand the fearless pursuit of the class struggle has always proven the most effective preventative of foreign invasions.

He continued to be a major critic of the Social-Democratic leadership under Karl Kautsky and its decision to acquiesce in going to war. Liebknecht's parents were second cousins; his maternal great-grandmother was the sister of one of his paternal great-grandfathers. See also
Luxemburgism
Ture Nerman & Zeth Höglund
Karl Liebknecht (film).

Liebknecht and Luxemburg were murdered. [About this sound] Karl Liebknecht (help·info) (13 August 1871 Leipzig Saxony Germany – 15 January 1919 Berlin Germany) was a German socialist and a co-founder with Rosa Luxemburg of the Spartacist League and the Communist Party of Germany.