Most political flags are designed. The red flag was not so much designed as seized. A plain rectangle of red cloth, the cheapest and most visible banner a crowd can improvise, it became the emblem of socialism and the labour movement through a century of French insurrections, Welsh riots, and one short-lived revolutionary government, and it did so by inverting its original meaning. The flag that once ordered crowds to disperse became the flag the crowds carried.
The signal of no quarter
Red flags signalled danger long before they signalled politics. Medieval warships flew long red streamers, called baucans, to announce that a fight would be to the death and no quarter given; English and French fleets both understood the code by the fourteenth century. Pirates used a plain red flag the same way, and it was in some ways more feared than the black one. On land, red flags marked gunpowder magazines, flood tides, and auctions. The common thread was blunt: pay attention, something dangerous is here.
Revolutionary France made this official. A law of October 1789 established the red flag as the legal signal of martial law. When municipal officers hung it out, a gathering became an illegal assembly and could be dispersed by force. The red flag, at this point, belonged to the government.
The Champ de Mars and the inversion
On July 17, 1791, a crowd gathered on the Champ de Mars in Paris to sign a petition calling for the removal of King Louis XVI, who had just been caught trying to flee the country. The mayor declared martial law, the red flag went up, and the National Guard under the Marquis de Lafayette fired into the crowd. The exact toll is unknown; estimates of the dead run from a dozen to fifty.
The radical Jacobins responded with one of the great acts of symbolic judo. They adopted the red flag themselves, flying it in honour of the "martyrs' blood" spilled beneath it and calling it the martial law of the people against the government. From then on, in France and beyond, the red flag was the banner of insurrection. Red caps and red cockades ran through the Revolution's later years, and the association between red and popular revolt survived Napoleon, the Restoration, and every attempt to suppress it.
The flag's first documented outings as a specifically working-class banner came in the next generation. During the Merthyr Rising of 1831, ironworkers in South Wales marched under a flag dipped in animal blood, an event Welsh historians have claimed as the first time the red flag was raised as a banner of workers' power. In Paris, insurgents flew it on the barricades of the June Rebellion of 1832, the uprising at the centre of Les Misérables.
1848 and the tricolour
In February 1848 revolution toppled the French monarchy again, and the crowds that made the Second Republic wanted the red flag as its national flag. The poet-politician Alphonse de Lamartine faced them down on the steps of the Hôtel de Ville on February 25 with one of the century's famous speeches: the tricolour, he said, had carried the name and glory of France around the world, while the red flag had only been dragged through the people's blood around the Champ de Mars. The tricolour stayed. The red flag, definitively rejected by the state, became the property of the socialist left, and the revolutions that spread across Europe that year carried it with them.
The Paris Commune finished the job. For ten weeks in the spring of 1871, the revolutionary government of Paris flew the plain red flag as its official flag, the first government to do so. The Commune died in the Bloody Week of May 1871, with perhaps ten to twenty thousand Communards killed, and the massacre fixed the flag's meaning permanently. Honouring the Commune meant honouring the red flag. When the international socialist movement organized itself in the 1880s, and when the Second International called the first May Day demonstrations in 1890, the question of which banner to march under had long been settled.
The song
The flag has an anthem, and the anthem has a grievance. In December 1889 Jim Connell, an Irish socialist living in London, wrote six verses on the train home from a lecture on the great London dock strike, taking inspiration from the strike, the Paris Commune, Russian revolutionaries, and the Irish Land League. "The people's flag is deepest red / It shrouded oft our martyred dead." Connell intended the words for "The White Cockade," a lively Jacobite air. To his lasting irritation, the movement sang them instead to "O Tannenbaum," a slow German carol tune. The dirge version stuck.
"The Red Flag" became the unofficial anthem of the British Labour Party. Delegates sing it at the close of the annual conference, and newly elected Labour MPs sang it in the House of Commons in 1945 after Clement Attlee's landslide, to the visible discomfort of the Conservative benches.
From banner to state flag
In the twentieth century the red flag moved from the barricade to the flagpole of the state. The Soviet Union adopted its flag in 1923: plain red, with a gold hammer, sickle, and star in the canton. Nearly every communist state that followed built on red. The People's Republic of China adopted the five-star red flag in October 1949. Vietnam's red flag with a single gold star, first flown by insurgents in 1940, became the national flag in 1945 and remains so. Albania put its black eagle on red; Mongolia, Yugoslavia, and others worked red into their designs.
The plain, undecorated version never went away. It still leads May Day marches, flies over strike pickets, and hangs from union halls from São Paulo to Kolkata. A century of state communism gave the red flag heavier baggage, and several post-Soviet countries now restrict communist symbols derived from it. But as a piece of cloth it remains what it became in 1791: the simplest possible way for a crowd to say it has had enough.
References
[1] "Red flag (politics)," Wikipedia. https://en.wikipedia.org/wiki/Red_flag_(politics)
[2] Age of Revolution, "Red Flag," object history. https://ageofrevolution.org/200-object/red-flag/
[3] "Champ de Mars massacre," Wikipedia. https://en.wikipedia.org/wiki/Champ_de_Mars_massacre
[4] "Merthyr Rising," Wikipedia. https://en.wikipedia.org/wiki/Merthyr_Rising
[5] "The Red Flag" (song), Wikipedia, on Jim Connell and the anthem's history. https://en.wikipedia.org/wiki/The_Red_Flag
[6] Alphonse de Lamartine, speech at the Hôtel de Ville, Paris, February 25, 1848.
[7] "Paris Commune," Wikipedia. https://en.wikipedia.org/wiki/Paris_Commune