Germany's relatively benign China policy, as shaped by Bismarck changed, under later German chancellors during the reign of Wilhelm II. After German naval forces were sent in response to attacks on missionaries in Shandong Province, Germany negotiated in March 1898 at the Convention of Peking a 99-year leasehold for Kiautschou Bay and began to develop the region. The period of the Boxer Rebellion of 1900 proved the low point in Sino-German relations and witnessed the assassination of the German minister to China, Baron Clemens von Ketteler and other foreign nationals. During and after the campaign to defeat the Boxers, troops from all participating states engaged in plundering and looting and other excesses, but the Germans were the worst. The tiny contingent of troops then in North China wanted to exact retribution for the murder of the diplomat. On 27 July 1900, Wilhelm II spoke during departure ceremonies for the German contribution to the international relief force. He made an impromptu but intemperate reference to the "Hun invaders" of Continental Europe, which was later resurrected by Allied propagandists to attack Germany during World War I and World War II.