Germany was a Christian country - the majority identified with Protestantism and a significant minority with Roman Catholicism.
Bismarck viewed Roman Catholics as a danger to the German state and responded with a 'culture struggle' designed to make sure that the Catholic Church in Germany was loyal to the German state.
Laws were introduced giving the state the right to veto the appointment of Catholic priests and bishops. Catholic priests resisted this, leading to arrests and imprisonment.
The main liberal parties refused to defend the rights of Catholics as they were convinced that Catholicism was a threat to true German culture.