Why did the gap between the wealthiest and poorest Americans steadily get larger in the decades after 1970?

Since the 1970s, there has been an income inequality in America.

Explanation:

The years from the end of World War II into the 1970s were ones of strong economic growth and prosperity. At the beginning of the 1970s, economic growth reduced, and the income gap increased.

Income inequality has risen steadily among all Americans since the 1970s. In the late 1970s, tax changes, federal monetary policies, deregulation, de-unionization, and other policies reduced wages and employment. Income among the middle and lower parts decreased sharply, while incomes at the top extended to grow strongly.