Zongli Yamen
In 1859, following China's defeat in the Second Opium War, Prussia sent the Eulenburg Expedition to negotiate commercial treaties with China, Japan and Siam. On 2 September 1861, Friedrich Albrecht zu Eulenburg and a representative from the Zongli Yamen signed the , which opened formal commercial relations between China and Prussia, which represented the German Customs Union. Prussia would later on become the dominant and leading part of the newly founded German empire. The treaty would govern Sino-German relations until World War I, when the Republic of China repudiated the treaty unilaterally.