In 1792, the War of the First Coalition pitted the monarchies of Europe against Revolutionary France in a war to prevent the spread of the Enlightenment ideas of self-rule by its citizens. The US Constitution, the French Declaration of the Rights of Man and of Citizen, and the recent Polish and French Constitutions of 1791, were direct threats to their authority. So the armies of Great Britain, Prussia, Russia, Austria and Spain invaded France.
With the loss of so much of their officer corps (who were mostly noblemen), the War of the First Coalition began poorly for the French. The armies of her enemies descended upon the traditional invasion corridors into the country. In Alsace/Lorrarine, the Prussian army approached, and the French were not prepared. The mayor of the fortress city of Strasbourg asked a young captain, Claude-Joseph Rouget de Lisle, to write a song to rally the troops of the garrison. On 24 April 1792, he composed the “War Song for the Army of the Rhine”. The song was a bloody and zealous anthem to the revolution and quickly spread across the country.
Toward the end of May, Provencal volunteers for the French National Guard arrived in Paris from Marseille. The desperately needed troops marched into the city singing Rouget’s song. They were such a sight and sang with such gusto that the song acquired the name we know of it today, the French National Anthem,