Following a severe postwar depression in 1920 and 1921, the American economy boomed through the remainder of the decade. Mechanization of production; investment; and new industries such as broadcasting, motion pictures, and the automobile industry drove the economy. Oligopoly the control of an entire industry by a few giant firms eliminated competition; Americans accepted the idea that size brought efficiency and productivity. While many businesses boomed, "sick" industries such as textiles, coal mining, agriculture and railroads, dragged the economy down. Not all Americans shared in the economic boom; the gap between rich and poor widened.