which countries were part of this empire?
The empire  consisted of 26 states, most of them ruled by royal families.
German Empire
 consisted of 26 states, most of them ruled by royal families. 
paragraph 231 of the versailles treaty dealt with It was the opening article of the reparations section of the Treaty of Versailles, which ended the First World War between the German Empire and the Allied and Associated Powers. who wrote it? Norman Davis and John Foster Dulles
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German Empire [SEP] Introduction
Berlin remained its capital, and Bismarck, Minister-President of Prussia became Chancellor, the head of government. As these events occurred, the Prussian-led North German Confederation and its southern German allies were still engaged in the Franco-Prussian War. The German Empire consisted of 26 states, most of them ruled by royal families. They included four kingdoms, six grand duchies, five duchies (six before 1876), seven principalities, three free Hanseatic cities, and one imperial territory. Although Prussia was one of four kingdoms in the realm, it contained about two thirds of Germany's population and territory. Prussian dominance had also been established constitutionally.