The Boxer Rebellion, which took place at the start of the 20th century, was a 3-way power struggle between Chinese peasants, the Boxers (a xenophobic, anti-Christian, anti-modernization, mystic religious group), the Qing Empire and (mostly) Western foreign powers.

The United States desired to set up commercial operations in China (Open Door policy) before the rebellion to compete with other European powers, especially British dominance, but had no interest in involving itself in military matters. However, after realizing how serious the rebellion was becoming, the McKinley Administration through Secretary of State John Hay, approved military action combined with European powers (the Eight Nation Alliance included Great Britain, Austria-Hungary, Germany, Italy, Russia, France, Japan & USA), despite its diplomatic tradition of avoiding entangling alliances, and the policies of the Monroe Doctrine, to avoid getting involved in the politics of European colonial powers.

The defeat of the Qing Empire in Tianjin and siege of Beijing by the Boxer rebels in July 1900 caused major world powers to intervene more directly, and the Eight Nation Alliance arrived in Beijing (Peking) to lift the siege.

US Troops were sent from the naval base in the Philippines and included the 9th Infantry, 14th Infantry, 6th Cavalry, 5th Artillery regiments and a Marine battalion under the command of Lt. Gen Adna Romanza Chaffee and was known as the "US Army China Relief Expedition". This was the first time US forces fought on Chinese soil, and also set a historical precedent where the president could intervene in a sovereign nation's affairs without the express authorization from Congress.

Japan sent the largest contingent of troops: 20,840 and 18 warships, but they also suffered a disproportionate number of casualties: more than half of allied casualties in Tianjin, and almost two-thirds of the losses in Beijing. The reason is that (according to a British military observer), the Japanese were aggressive, used densely-packed formations and were over-willing to attack.

The British was also engaged in the Boer conflict at the same time, so they had limited troops available, and had to rely on the 'China Squadron' and troops from India. They were the third largest contingent after the Japanese.

The Russians had the second largest force, of 12,400.

Austria-Hungary sent a single cruiser and sent some sailors to defend positions in Tianjin.

The Germans initially had a garrison of about 2,000 men around Qingdao (Tsingtao), and sent a larger force of around 15,000 later in the struggle, but they arrived too late to take part in any major action.

The French sent three battalions and a brigade of marines.

The Italians had around 2,000 troops, initially made up of sailors from warships and later included troops dispatched from Italy.

After the rebellion was culled, the signing of the Boxer Protocol of 1901 which was signed between the Eight Nation Alliance and the Qing Empire then allowed Britain and the USA (and to a lesser extent the other 6 nations) to have a great deal of influence in Beijing and to be in control of how the country could be partitioned.

Before the rebellion, there was a lot of discussion in the media about the rebellion, and The Washington Post, for example, had a field day publishing reports about it, mostly factually incorrect, as they had no reporters on the ground; there was a major disconnect between the information in China and the US public and it could be argued that the public opinion in the US was shaped by American and Chinese interest groups to support the rebellion and draw US forces into the war.

After the rebellion, there was a great deal of debate about the US involvement. It was revealed that a number of atrocities were committed by foreign troops, and precious artifacts and treasures were heavily looted from places like the Forbidden City. Mark Twain gave his famous "I am a Boxer" speech that mocked and criticized Christian missionaries and the US government involvement in China. Furthermore, the reparations payments on China were extremely high and they were forced into virtual disarmament.