The result of these commercial, religious, and political connections was that relations between the U.S. and China were good for much of American history. In the late 1800s, the powers of Europe and Japan were expanding their colonial empires. Some of them wanted to break China up into colonies, but U.S. leaders believed it would be better for American interests if China remained independent and united. So, the U.S. supported an "Open Door" policy, which meant that China would have an "open door" to foreign investment and trade, but no nation would control it. This was a fundamental part of U.S. policy toward China through the end of World War II, and it kept China from fragmenting and limited foreign exploitation.

When Japan tried to expand its empire in the early 1930s, the U.S. believed this violated the "Open Door" policy. America's opposition to Japanese expansion ultimately led the U.S. to deploy its Pacific Fleet to Pearl Harbor, where Japan attacked it on December 7, 1941. Even before then, American volunteers, such as the famed "Flying Tigers," were fighting in China. When the U.S. entered the war, it flew squadrons of B-29s from China, and sent it substantial amounts of aid. After the war, it was the U.S. that insisted that China be included as one of the five Permanent Members of the U.N. Security Council.

Sino-American relations were not always good. The U.S. passed the Chinese Exclusion Act in 1882; this marked the first time the U.S. had restricted immigration. The U.S. later prohibited Chinese immigrants from obtaining citizenship because of their race, which it had never done before. When U.S. forces joined other nations in protecting Americans and Europeans in Peking during a rebellion (called the Boxer Rebellion) that began in 1899, some Chinese branded the U.S. a foreign exploiter. Yet, after the war, the U.S. used some of the reparations that China paid to establish the "Boxer Indemnity Scholarship Fund," an influential education program in China.The longest period of Sino-American tension came after the founding of the mainland People's Republic of China (the PRC) in 1949, when Mao Zedong's Communists drove Chiang Kai-shek's Nationalists onto the island of Taiwan. American and Communist Chinese forces fought each other during the Korean War, which began in 1949. Communist threats against Taiwan in the 1950s drove the U.S. and the PRC to the brink of nuclear war. The U.S. went to war in Vietnam in part to prevent the expansion of Chinese Communism.

But in 1972, President Richard Nixon reestablished relations with the PRC. Nixon hoped to use better relations with China to balance the rising power of the Soviet Union. Chinese leaders were receptive because they too were worried about the USSR. Mao's successor, Deng Xiaoping, sought to bring China closer to the West, but he also believed that the Communist Party had to remain in power. So even as he opened the economy, he sought to prevent political liberalization at home. The result was the start of China's economic rise, but also the killing of protestors in Tiananmen Square in 1989.

The Tiananmen Massacre and the end of the Cold War reshaped U.S. relations with China. While the U.S. and China grew closer economically, their foreign policies diverged. When NATO mistakenly bombed the Chinese embassy in Belgrade in 1999, during its war in the Balkans, it convinced many Chinese that the U.S. was trying to contain China. At the same time, China's lack of respect for human rights, its efforts to steal American technology, and its growing military power raised American doubts about whether the U.S. could work with China.