Why did Otto von Bismarck ban the Social Democratic Party from 1878 to 1890?

Otto von Bismarck banned the Social Democratic Party from 1878 to 1890 primarily because he viewed the socialists as a grave threat to the stability of the German Empire, labeling them and other groups as enemies of the empire (Reichsfeinde).12

Bismarck’s motivations included:

• Political Strategy: He believed that every political system required an enemy to maintain cohesion and secure conservative majorities. After the Kulturkampf against the Catholic Centre Party failed to achieve its goals, he shifted his focus to the socialists.12
• Ideological Opposition: Bismarck held an uncompromising hatred for socialists and anarchists, viewing them as a force bent on murder and pillage. He perceived their questioning of the empire's capitalist character as a direct challenge to his vision of a united Germany.2
• Opportunism: Following two failed assassination attempts against Emperor William I in 1878, Bismarck exploited the public outcry by unjustly blaming the socialists. This allowed him to dissolve the Reichstag, win an election on the cry of "the social peril," and pass the Anti-Socialist Law.12

While the ban restricted party meetings and publications, Bismarck simultaneously implemented social security measures to try to win workers away from radicalism, though this two-pronged strategy ultimately failed to curb the party's growth.12