“The marked increase in the popular participation in securities transactions has definitely placed under the control of financiers the wealth of the Nation.” Thus concluded the Senate’s report into the causes of the stockmarket crash of 1929. The world is again in an age of truly powerful financiers. Some giants of today simply reflect the size of America’s economy. JPMorgan Chase, the largest bank, is big because America is. But others owe their heft to how the structure of markets has changed.