Five days of work and two days of play is how most Americans structure their lives. But the 40-hour, 5-day work week wasn’t enshrined until the passage of the Fair Labor Standards Act in 1938. That law was the culmination of more than a century of American workers fighting for shorter hours, better wages and safer working conditions.

“At the turn of the 20th century, it was not uncommon for most Americans to work 60 or more hours a week,” says Joseph McCartin, a labor historian at Georgetown University.

In 1898, Massachusetts published a “labor bulletin” tracking the wages and hours of domestic workers in the commonwealth. Domestic cooks at the time worked between 78 and 83 hours a week for about 9 cents an hour. They got Sundays off and sometimes a half day on Saturdays. Some factory workers in Massachusetts were slightly better off; according to state law, women and children could only work a maximum of 58 hours a week in textile mills.

“In many ways, the idea of limiting working hours and days extends back to the very beginning of the American labor movement,” says Erik Loomis, a labor historian at the University of Rhode Island.

The rallying cry of the 19th-century labor movement was “Eight hours labor, eight hours recreation, eight hours rest,” a phrase first coined by Robert Owen, a Welsh textile manufacturer turned labor reformer.

The 8-hour movement picked up steam after the Civil War when soldiers returned home to rapidly industrializing towns and cities. They were joined by millions of formerly enslaved people fighting for fair wages and humane working conditions.

Chicago was a hotbed of labor activism in the mid-19th century. Chicago workers, exhausted by the typical 12- or 14-hour workday, were some of the first to successfully lobby state representatives to pass an eight-hour limit for Illinois workers in 1867. Unfortunately, the Illinois law had loopholes that allowed employers to negotiate for more hours, which rendered it ineffective.

The next big push came on May 1, 1886, when Chicago unions and political activists called for a nationwide “May Day” strike for the 8-hour day. More than 10,000 people gathered in Chicago for what was supposed to be a peaceful demonstration. Tensions escalated between strikers and police, resulting in the death of four demonstrators. In response, rioters and anarchists took to the streets on May 4, a violent clash that ended with a deadly bombing in Chicago’s Haymarket Square.

The 1886 “Haymarket Affair” was a painful setback for the 8-hour movement, which didn’t fully recover until World War I.

In 1916, as politicians debated entry in World War I, more than 400,000 American railroad workers threatened to strike unless they were given an 8-hour workday. The massive nationwide strike would have crippled America’s industrial production on the eve of war.

When negotiations broke down between the railroads and the striking workers, President Woodrow Wilson and Congress intervened to avert a national crisis. The result was the Adamson Act of 1916, the first federal law mandating an 8-hour workday, if only for a single industry.

When the United States finally entered the war in 1917, the resulting labor shortage gave workers more leverage to demand fewer hours and shorter work weeks.

“In the first six months of America's involvement in the war, more strikes took place in the U.S. than during any previous period in American history,” says McCartin, co-author with Melvyn Dubofsky of Labor in America: A History.

Fearing that strikes would slow the production of essential wartime equipment, President Wilson created the National War Labor Board to intervene in labor disputes and force employers to recognize collective bargaining. The result was a brief “golden age” for American workers during 1917 and 1918, including widespread adoption of the 8-hour day.

When the war ended on November 11, 1918, industrialists tried to roll back the gains made by workers by increasing hours, but they were met with fierce opposition. Emboldened American workers organized 3,000 strikes in 1919 involving more than 4 million laborers.

“Employers realized that the genie had been let out of the bottle during the war and couldn't be entirely stuffed back in,” says McCartin. “They couldn't return to the status quo and try to force workers to work the way they did prior to the war.”

In 1913, Henry Ford’s Highland Park Plant became the first to employ the company’s groundbreaking assembly line technology. While the assembly line was able to produce cars radically faster and cheaper than ever before, it was also backbreaking, repetitive work. Just months after opening, workers were quitting at such a fast rate that labor turnover at Highland Park reached 380 percent.

“Ford was dealing with what so many industries dealt with at the time, which was massive turnover,” says Loomis. “These jobs were terrible and nobody wanted to stay at them. He decided to embrace the ideas of scientific management and make a deal with the workforce.”

Ford’s irresistible offer was a $5, 8-hour workday—almost twice the pay for less work than before. As part of the deal, workers at Highland Park had to consent to inspections by the company’s “Sociological Department,” which flagged workers for drinking or reading “radical” (pro-union) material.

As early as 1922, the Ford Motor Company took steps toward the creation of a 40-hour workweek—five 8-hour days and a two-day weekend. “Every man,” said Edsel Ford, the founder’s son, “needs more than one day a week for rest and recreation.”

The decision was about more than just happy workers, says McCartin. It was part of an economic philosophy later called “Fordism.” Under Fordism, mass production requires mass consumption. Ford wanted his workers to be well-paid and well-rested so they would use their leisure time to buy more things, including his cars.

Ford officially adopted a five-day, 40-hour workweek in 1926. Since Ford was the most influential industrialist of his day, other large companies followed his lead.

“While a leading automaker like Ford certainly influenced what some other corporate leaders did in their enterprises, the 40-hour week wasn’t widely adopted until the government made it the law of the land,” says McCartin. “And that happened with FDR and the Fair Labor Standards Act.”

When President Franklin D. Roosevelt was elected in 1932, the nation was in the throes of the Great Depression. Unemployment was at 25 percent—one in every four Americans was out of work. To meet this incredible challenge, FDR appointed Frances Perkins as his Secretary of Labor. Perkins was the first female cabinet member in U.S. history and a committed workers-rights advocate.

Together with allies in Congress, FDR and Perkins passed the National Industrial Recovery Act in 1933. The sweeping New Deal legislation addressed the most pressing labor issues of the day. It established a federal minimum wage of $12 to $15 a week, prohibited child labor younger than 16 years old and capped the work week at 40 hours.

But the trailblazing labor law didn’t survive. In 1935, the Supreme Court struck down the National Industrial Recovery Act as unconstitutional. Perkins and FDR spent the next three years fighting the courts and critics in Congress to claw back the gains that were lost. A major victory came in 1936 with the Public Contracts Act, a law that required most federal contractors to adhere to a 40-hour work week.

Finally, in 1938, FDR and Perkins were able to push through the Fair Labor Standards Act (FLSA). The original version of the law capped the work week at 44 hours. It also created the first federal rules for overtime pay. Any hours worked beyond 44 must be compensated at one-and-a-half times the regular hourly rate.

The FLSA stipulated that the work week would be reduced to 42 hours after one year and then 40 hours after two years. The 40-hour, 5-day workweek has been the standard in America ever since.