Why did Otto von Bismarck introduce tariffs on grain and iron in 1879?

Otto von Bismarck introduced protective tariffs on grain and iron in 1879 for a combination of economic, social, and political reasons:

• Economic Protection: Following the global economic depression of 1873, German agriculture and industry suffered significantly. Bismarck sought to protect domestic iron and steel production to ensure national strength, while also shielding German agriculture from the influx of cheap American and Russian grain.12
• Social and Political Stability: Bismarck aimed to secure the support of the Junker estate owners and major industrialists, forming an alliance to forestall the rise of social democracy and prevent further political liberalization. He viewed agricultural workers as a vital element for the military and believed these protections would insulate the landed elite from market uncertainties.12
• Financial Independence: Bismarck wanted to increase imperial revenue through indirect taxes to reduce the government's dependence on financial contributions from individual states and to escape the political control of the National Liberals in the Reichstag.1