According to Social Darwinian thinkers, human existence was conceived as a pitiless struggle in which the strong prevailed and the weak were cast aside. This discourse could be applied to racial struggles, as it often was, as well as to predatory business practices.
Titans of industry such as Andrew Carnegie, who nearly monopolized steel production, ruthlessly crushed their competitors through vertical and horizontal methods. Carnegie systematically gained control of the supply chain for steel producers in the Northeast, then used his power to drive out competitors by underpricing. Additionally, Carnegie used brutal force to crush an attempt to unionize his largest and most profitable steel mill, at Homestead in Pennsylvania. While he also endowed universities and libraries with millions as part of his conviction that the wealthy had an obligation to society, his understanding of business as a death struggle was typical of not only economic theorists but social scientists of his time.
Others applied Social Darwinism to what they saw as a continuous struggle for racial domination. Perceiving that whites were victorious in this struggle, they believed that miscegenation, or race mixing, would lead to a weakening of the white race. They thus sought to, in the South, formalize Jim Crow laws, implementing "one drop rules" to define blackness in many Southern states. Congress acted, in 1884, to eliminate competition from Chinese immigrants in the West through the Chinese Exclusion Act, and a "Gentlemen's Agreement" with the Japanese government similarly limited Japanese immigration.
By the 1920s, whites feared the influx of radical politics, which they associated with eastern Europeans. Accepting some of the conclusions of eugenicists, Social Darwinists, and other racists, they even began to imagine eastern Europeans as a different, inferior race, that had to be eliminated. They thus placed quotas in 1921 and 1924 that limited the influx of eastern and southern Europeans.