The North German Confederation Treaty (in German Augustbündnis, or Alliance of August) (also called the North German Federation Treaty and the Treaty of 18 August 1866) was the treaty between the Kingdom of Prussia and other northern and central German states that initially created the North German Confederation, which was the forerunner to the German Empire. This treaty, and others that followed in September and October, are often described as the August treaties, although not all of them were concluded in August 1866.
The treaties followed the Austro-Prussian War of Summer 1866, after which the German Confederation of 1815 was dissolved. The treaties established:
- a military alliance, and
- an agreement to transform the alliance into a nation state, based on the Prussian reform plan for the German Confederation
The German states involved arranged the election of a North German parliament in February 1867. The parliament on the one hand, and the governments on the other, agreed on a constitution for the North German Confederation on 1 July 1867. This Confederation, a federal state, was expanded in 1870–71 with the south German states and became the German Empire. The August treaty of 1866, therefore, can be seen as the first legal document that established the modern German nation state.