In the dispute over neighbouring Holstein which culminated in the 1866 Austro-Prussian War, Frederick Francis II supported the Kingdom of Prussia, whom he aided with Mecklenburg-Schwerin soldiers. His grand duchy began to pass more and more under Prussian influence. In 1867 he joined the North German Confederation and the Zollverein. In the Franco-Prussian War (1870–1871), Prussia again received valuable assistance from Grand Duke Frederick Francis II, who was an ardent advocate of German unity and held a high command in her armies. In the course of the German unification in 1871, Mecklenburg-Schwerin and Mecklenburg-Strelitz became states of the German Empire. There was now renewed agitation for a more democratic constitution, and the German Reichstag parliament gave some countenance to this movement.