Trade routes between China and the United States were established in the early nineteenth century, with traders from Philadelphia selling opium to the Chinese as early as 1810.
The Qing Dynasty of China hoped to end the opium trade, which European traders imported from the then British colony of India. The British were the victors, and the opium trade continued.
This was the treaty between China and the United Kingdom that ended the First Opium War. The treaty opened five additional Chinese ports to Western trade, required that European traders accused of crime be charged by their country, gave control of the island of Hong Kong to the British, etc.
The treaty granted religious freedom to Americans in China, recognised China's right to take private land within the bounds of the country's territory for public use (eminent domain), etc. It was signed in Washington in 1868, but not ratified in China until the next year.
U.S. Secretary of State John Hay sent notes to major world powers (Great Britain. France, Russia, Italy, Japan, and Germany) asking them to formally uphold uphold Chinese territorial and administrative integrity.
Chinese protest of the Paris Peace Conference.