In a column adapted from his new book, “Enemies: A History of the FBI,” Tim Weiner remembers the 1920 Wall Street bombing that made J. Edgar Hoover’s career:

Shortly after noon on Thursday, Sept. 16, 1920, a powerful bomb hidden in a horse-drawn wagon exploded at the corner of Wall and Broad Streets in Manhattan. It was a pleasant late-summer day, and throngs of people had been out enjoying a lunchtime stroll, a brief respite from the great money machine, the center of American capitalism.

Now blood ran in the streets where the first U.S. Congress had convened and the Bill of Rights became law.

Shrapnel scarred the walls and shattered the windows of J.P. Morgan and Co., America’s most formidable bank. The bomb killed at least 38 people and injured roughly 400. It was the deadliest terrorist attack in U.S. history, a distinction it held for 75 years. Its force reverberates today.

In Washington at that hour, J. Edgar Hoover, 25 years old, was putting the finishing touches on the federal government’s first counterterrorist force, the General Intelligence Division. Hoover wrote that he intended to combat “not only the radical activities in the United States” but also those “of an international nature”; not only radical politics, but “economic and industrial disturbances” as well.

He said the government could not handle “the radical situation from a criminal prosecution standpoint.” The law was too weak a force to protect the country. He believed the U.S. needed a new weapon to fight communists, anarchists and the forces he later called “red fascism.” Only secret intelligence and countersubversion could detect and disrupt the threat from the left and protect America from attack.

Hoover had been fighting the threat since joining the Justice Department during World War I. His war never ended.