Passage: This open opposition against the party line put Liebknecht at odds with some party members around Haase who were against the war bonds themselves. In February 1915, at the instigation of the SPD party leadership, Liebknecht was conscripted for military service to dispose of him, the only SPD deputy to be so treated. Because of his attempts to organise objectors against the war, he was expelled from the SPD, and in June 1916, he was sentenced on a charge of high treason to four years in prison. While Liebknecht was in the army, Rosa Luxemburg wrote most of the "Spartacus Letters". After serving a prison sentence, she was put back in jail under "preventive detention" until the war ended.

Question: What crime was Liebknecht sent to prison on?
high treason