In France, the abolition of the monarchy was carried out by the National Convention through a proclamation issued on September 21, 1792, during the French Revolution, declaring the republic the same day. The abolition of the monarchy was a direct consequence of the August 10th events, when the Paris Commune stormed Tuileries Palace, massacred the Swiss Guards, and arrested the King Louis XVI.
Background to the abolition of monarchy
Under the Constitution of 1791, France would function as a constitutional monarchy. This meant that the King had to share power with the elected Legislative Assembly. However, he still retained his royal veto and the ability to select ministers. The Legislative Assembly had first met on October 1, 1791, but it had degenerated into chaos in the political strife between the constitutional monarchists and the republicans (Girondists and Jacobins) less than a year later. Thus, on the night of August 10, 1792, insurgents, supported by a new revolutionary Paris Commune, had assailed the Tuileries Palace and massacred the Swiss Guards who were assigned for the protection of the king. The royal family had ended up prisoners and a rump session of the Legislative Assembly had suspended the monarchy. More than a third of the deputies were present, almost all of them Jacobins.
What had remained of a national government depended on the support of the insurrectionary Commune. The Commune had sent gangs into the prisons to try arbitrarily and butchered 1400 victims, addressing a circular letter to the other cities of France inviting them to follow this example. As a result, the Legislative Assembly could offer only feeble resistance. This situation had persisted until the National Convention, which was charged with writing a new constitution, met on September 20, 1792, and became the new de facto government of France. The next day it abolished the monarchy and declared a republic. This date was later retroactively adopted as the beginning of Year One of the French Republican Calendar.