The main objective of the National Origins Act of 1924 was to favor the immigration from Northern and Western Europe. The government did this to tighten the 1921 quota formula for immigration.
The Open Door policy was one United States policy from 1899 that aimed keeping equal rights for countries trading with China. The area which U.S. wanted to keep from gaining too much control was Europe. That since the Opium War was exploring and keeping privileged trades in China.
The conflict example of European/Western intrusion in China before the Boxer Rebellion is Opium Wars. The Boxer Rebellion occurred around 1900, the Opium Wars was between Western Countries and Qing Dynasty, the Western fought for territory and commercial control of China and won the war creating an equal state of trading for European Countries during 1800.
At Yalta, Roosevelt and Churchill discussed with Stalin the conditions under which the Soviet Union would enter the war against Japan and all three agreed that, in exchange for potentially crucial Soviet participation in the Pacific theater, the Soviets would be granted a sphere of influence in Manchuria following.
