The German electoral system makes it very difficult for any one party to form a government on its own. This has only happened once in 56 years. An alliance of parties is the general rule. So that the voters know which partner the party they voted for is considering governing with, the parties mostly issue coalition statements before embarking on the election campaign. By voting for a particular party citizens thus express on the one hand a preference for a specific party alliance, and on the other determine the balance of power between the desired future partners in government.