Individuals cannot be independent of society. When society changes, its members have to modify their behavior patterns. Thus when exploring the content of individualism, we cannot ignore its social background. Before the Civil War, the newly independent country remained an agricultural and democratic society because of the rich land resources, equal social condition and the dissipation of feudalism. Each individual was rather isolated, and struggled to survive against the natural environment, leading to the birth of agricultrual individualism. After the Civil War, the fruits of industry made the US an affluent society. Economic individualism claimed that people should enjoy more freedom to compete with one another for their wealth. After the era of New Deal, society became increasingly complicated. Supporters of old individualism, which valued competence, found it a hindrance to moving toward a more perfect society. Collaboration and unity might be the new formulas to help individuals survive well in the new society.