In the early 20th Century, the United States has no workplace safety laws.

Machines in garment factories could be cruel taskmasters, as could employers.

In the early 20th Century, many female immigrants worked in garment factories. Some were girls as young as ten, whose families had chosen America for its promise of a better future.

The 1911 Triangle factory fire killed 146 and changed beliefs about workplace safety. New Yorkers from all walks of life came to pay tribute to the victims.

Watch Chapter 1 of Triangle Fire.

On March 25, 1911, a fire broke out in the Triangle Shirtwaist Factory in New York's Greenwich Village. By the time the fire had burned itself out, 146 people were dead. The landmark legislation that followed gave New Yorkers the most comprehensive workplace safety laws in the country.

Author Kirstin Downey on the labor rights activist Frances Perkins, who would go on to become the secretary of labor and the first woman in a U.S. Cabinet.

Watch a preview of Jimmy Carter.

Jimmy Carter traces the ascent of an ambitious country boy from a peanut farm in Plains, Georgia, to the Oval Office; it examines the failings of Carter's political leadership in the context of the turbulent 1970s; and explores the role religion played in his career.

Ronald Reagan left the White House one of the most popular presidents of the twentieth century — and one of the most controversial.

A passionate ideologue who preached a simple gospel of lower taxes, less government, and anti-communism.

In a televised address to the nation, delivered on March 23, 1983, President Reagan announced his vision of a world safe from nuclear threat. His Strategic Defense Initiative (SDI), later dubbed "Star Wars" by the press, is an idea that remains controversial to this day.

In 1988, after two terms in office, Ronald Reagan left the White House one of the most popular presidents of the twentieth century -- and one of the most controversial. One by one, his opponents underestimated him; one by one, Reagan surprised them, rising to become a president who always preferred to see America as a "shining city on a hill."

An epic story of adventure, abandonment and human tragedy, The Greely Expedition tells of an 1881 scientific mission to the Arctic that ended with death and rumors of cannibalism.

Historian Michael Robinson talks about the American scientific landscape in the 19th century and the significance of The Greely Expedition.

On November 12, 1904, the first Bucyrus steam shovel arrived in Colón, able to excavate five cubic yards of spoil in a single scoop. Despite the efficiency of the steam shovel, the 50-year old rail system proved incapable of carrying that amount of spoil away.

In all, approximately 5 million bags and barrels of concrete went into building the Panama Canal's locks, dams, and spillways. The locks were engineered to be hollow and water tight, making them buoyant, so that the weight and pressure on the hinges would be significantly reduced. The locks at Gatun were 80 feet high, completely powered by electricity generated by a nearby hydroelectric spillway.

Stevens realized that building a sea level canal would doom the project to failure. His answer was to build a lock canal -- a highly mechanized and engineered waterway that would raise ships up over the continent through a series of lock chambers, ultimately solving the environmental challenges they were facing.

On December 10, 1913, after a final push of excavation, the unbroken waterway finally connected the Atlantic Ocean to the Pacific Ocean. The project had taken ten years and more than $350 million. To that date, it was the largest single federal expenditure in history. More than 5,000 workers lost their lives, but the successful completion defined the US as a superpower of the 20th century.

Upon the arrival of new Chief Engineer John Stevens, the rusty and decrepit Panama Railroad was by that time 60 years old. Stevens realized that he was unable to cart out the spoil at the same furious rate that the canal was being dug. He ordered all excavation in Culebra Cut to be temporarily halted and turned his attention toward the repair of the railroad.