What term best describes the u. s. government's policies towards businesses in the late 19th century?

The answer is "Laissez-faire".

Laissez-faire is the approach which depends on the possibility that administrations and the law ought not meddle with business, fund, or the states of individuals' working lives.  

In a laissez-faire economy, the main job of government is to keep any compulsion against people. Theft, extortion, and imposing business models keep the sound market powers from working.  

Laissez-faire policies require three things to work, which are capitalism, the free market economy, and rational market theory

c. wright mills's sociological imagination suggest investigating to explain this increase?