Each year, people across the globe take to the streets to commemorate International Workers' Day, or May Day.
In dozens of countries, May Day is an official holiday, and for labour rights campaigners it is particularly important.
In the United States, it is symbolic of past labour struggles against a host of workers' rights violations, including lengthy work days and weeks, poor conditions and child labour.
Why is International Workers' Day on May 1?
In the late-19th century, socialists, communists and trade unionists chose May 1 to become International Workers' Day.
The date was symbolic, commemorating the Haymarket affair, which took place in Chicago, in the US, in 1886.
For years, the working class - often forced to work up to 16 hours a day in unsafe conditions - had been fighting for an eight-hour workday.
Then, in October 1884, the Federation of Organized Trades and Labour Unions of the United States and Canada decided that May 1, 1886, would mark the first day that an eight-hour workday would go into effect.
When that day arrived, between 300,000 and a half-million American workers went on strike in cities and towns across the country, according to various historians' estimates.
Chicago, which was the nucleus of the struggle, saw an estimated 40,000 people protest and strike.
|Female workers in the May Day Parade in New York City in 1936 [File: New York Daily News Archive/Getty Images]|
Until May 3, the strike was well-coordinated and largely nonviolent.
But as the end of the workday approached, striking workers in Chicago attempted to confront strikebreakers at the McCormick Harvesting Machine Company. Large police contingents were protecting the strikebreakers, and officers opened fire on the striking workers, killing at least two.
As the police attempted to disperse the protesters on May 4 in Chicago's Haymarket Square, a bomb was thrown at them, killing seven officers and at least four civilians.
Police subsequently rounded up and arrested eight anarchists, all of whom were convicted of conspiracy. A court sentenced seven to death and one to 15 years imprisonment. Four were hanged, one committed suicide rather than face the gallows and two had their sentences commuted to life in prison.
Those who died are regarded by many on the left, including both socialists and anarchists, as the "Haymarket Martyrs".
The Haymarket affair galvanised the broader labour movement.
In 1889, the Second International, the international organisation for workers and socialists, declared that May 1 would from then on be International Workers' Day.
In the US, however, the eight-hour work day wasn't recognised until it was turned into law in 1916, after years of strikes, protests and actions in favour of it.
What is the holiday's history after 1916?
After the eight-hour day was initiated in the US in 1916, it was endorsed by the Communist International, an international coalition of socialist and communist parties, and by communist and socialist parties in various countries.
In that same year, as World War I continued, partial strikes and clashes with police in the US and several European countries were fuelled by massive anti-war sentiment as much as they were driven by the struggle for labour rights.
In 1917, as the US declared its involvement in the war, socialists and other leftists demonstrated against the bloodshed.
Marxist leaders across the globe - among them Rosa Luxemburg and Vladimir Ilyich Ulyanov, who is most widely known as Lenin - considered the war to be an example of capitalist, imperialist countries pitting members of an international working class against one another. They argued that workers should unite and wage a revolutionary war against the ruling classes in their own countries.
Four days after the revolution that toppled Tsarist rule in Russia, the eight-hour workday was introduced there by official decree.
What have been some of the most memorable International Workers' Day protests?
International Workers' Day is marked with celebrations, protests, strikes and commemorations around the world.
While the size and intensity of commemorations have ebbed and flowed over the years, several International Workers' Day commemorations stand out.
In the US in 1971, as the war in Vietnam continued under the presidency of Richard Nixon, protests in Washington, DC, spanned several days and included civil disobedience against the war.
Nixon sent in an estimated 10,000 troops and mass arrests were made, prompting accusations of civil rights violations. Police and security forces arrested more than 12,000 people, although most were eventually released without charges.
|In Berlin, Germany, May Day protesters clashed with police in 2009 [File: Getty Images]|
More recently, in 2006, a series of US-wide immigration reform marches continued on May 1, when organisers called for a strike they named a "day without immigrants". Protests had already drawn the participation of between 350,000 and 500,000 people in cities across the US.
In 2016, large May Day protests and marches were held in countries across the world. In the Turkish city of Istanbul, protesters clashed with police while trying to reach the city's iconic Taksim Square. At least one protester was killed and dozens arrested.
In Moscow, tens of thousands of Russians marched in a pro-Kremlin rally to commemorate the holiday, while left-wing groups held separate events in several Russian cities.
In Taipei, Taiwan's capital, labour unions took to the streets with a march to call on the government to reduce working hours and increase wages.
Thousands of people in the German cities of Berlin and Hamburg participated in public demonstrations. Protests against the far-right Alternative for Germany (also known as AfD) party were held in several German cities.
What should you expect in 2017?
With a growing protest movement against the policies of US President Donald Trump and increasing clashes between his supporters and opponents, there will be large demonstrations in several US cities, including New York, Chicago, Seattle and Washington, DC, among others.
In recent weeks, clashes between anti-fascist, or Antifa, activists and Trump supporters have increased in frequency and intensity. Two weeks ago in Berkeley, California, pro- and anti-Trump demonstrators fought in the streets, leading to multiple arrests and injuries.
On Monday, organisers from Movimiento Cosecha, an immigrant rights campaign, say an estimated 400,000 workers have committed to strike in the US.
The Democratic Socialists of America (DSA), a left-wing organisation, and several anarchist and anti-fascist groups plan to hold protests in New York City and elsewhere.
|Police and demonstrators clashed during Trump's inauguration on January 20 [File: Stephen J. Boitano/LightRocket via Getty Images]|
The Metropolitan Anarchist Coordinating Council (MACC), a New York City-based umbrella group, called for a mass anti-fascist and anti-capitalist bloc to stand in solidarity with immigrants, workers and prisoners.
Before the planned protests, police in Seattle, Washington, have prepared for violent confrontations. A police official says anti-Trump sentiment is likely to fuel the protests and lead to confrontations between his supporters and opponents.
"I think there's a great opportunity for crowd on crowd conflict," Seattle Police Capt. Chris Fowler said on Friday, according to local news. He said the police were preparing by practising crowd control techniques and the formation of barriers.
Protests are expected to be held in several countries across the globe.
In Nazareth, hundreds of Palestinian citizens of Israel, mostly from the local communist party, already marched to commemorate May Day on Saturday.
Source: Al Jazeera News