When an anti-foreign group known as "the Boxers" rose to rebel in China and occupy Peking, the US and many other nations undertook an international effort to relieve the foreign legations in Peking. The US was a full participant in the efforts but stated clearly that it was opposed to any foreign efforts to carve up China as a result of the rebellion.
The growing attempts of European powers and Japan to colonize China created resentment and growing opposition. This combined with a severe drought created unrest throughout China and led to the rise of the Boxer Movement. Their name came to their origins as part of martial society, that promoted conservative social norms, it soon turned its attention to foreign influence blaming it on the deterioration of Chinese society. They soon started attacking churches and other symbols of missionary presence in China.
Parallel to the rise of Boxers, the Chinese government attempted wide-ranging reform. That period is known as the Hundred Days of Reform. The Guangxu Emperor stood behind those reforms which were opposed by conservative members of the Chinese elite. They supported Empress Dowager Cixi who seized power. The Empress initially fought the Boxers but changed her position at the beginning of 1900. The Boxer movement the spread rapidly. Foreign legations were allowed by the Chinese government to send troops to defend their legations in Being. American Marines were a vital part of that force. The boxers burst into the foreign quarter of the city and surrounded the foreigners who were primarily being defended by US Marines.
The foreign legations decided to dispatch a rescue force of some 2000 meant who they thought would be more than sufficient to make there the way to Bejing and relieve the besieged legations. The army under British Vice Admiral Edward Seymour was not able to Bejing, and it had to be rescued by an additional foreign force. Meanwhile, in Beijing, a total of 473 foreigners, 409 soldiers, and 3,000 Chinese Christians held out in the Being Legation Quarter from June 20 onward.
Meanwhile, the foreign forces built up their forces in China intent on relieving the legations. Eventually, there was a force of 55,000, made up of Japanese (20,840), Russian (13,150), British (12,020), French (3,520), U.S. (3,420), German (900), Italian (80), Austro-Hungarian (75) and anti-Boxer Chinese troops. Twenty thousand of them made it towards Bejing. They were opposed by both 50,000 Boxer as well are regular Chinese troops. It was 120 kilometers to Bejing from Tianjin. The allied forces faced sporadic opposition by the Chinese. The most deadly foe was the head and humidity. The force reached Beijing on August 14, 1900. After brief but spirited defense the Chinese troops withdrew, and the Allied troops relieved the legations and occupied the city. For the next year, the Boxer continued to kill Christians throughout China and the allied forces that conquered large parts of Northern China committed their own atrocities against Chinese civilians.
The year of unrest was brought to an end by the signing of the Boxer Protocol, which called for the execution of the leaders of the Boxer movement and its supporters and the payment of reparations that totaled 450,000,000 taels of silver. The US used its part to provide scholarships for Chinese students.