In 1900, the United States sent the China Relief Expedition, comprised of the 9th and 14th Infantry regiments, elements of the 6th Cavalry and the 5th Artillery regiments, and a battalion of Marines to aid the Eight Nation Alliance in lifting the siege of Peking (modern Beijing). Earlier that year the Yìhéquán (Militia United in Righteousness), a populist group who detested both Christians and foreign interference, had risen in defiance of the government in Beijing. Known to the west simply as "The Boxers" they besieged the foreign legations and seized large portions of the Chinese capital.
Source: mudwerks