The Flight to Varennes

From Wikipedia:

Deprived of authority and in fact made virtually a prisoner by the initial events of the revolution from 1789, Louis XVI had for many months acquiesced in the decrees of the National Constituent Assembly. However, the Civil Constitution of the Clergy wounded both his conscience and his pride. From the autumn of 1790 onwards he began to scheme for his liberation. Himself incapable of strenuous effort, the King was spurred on by his wife Marie Antoinette, who keenly felt her own degradation and the curtailment of that royal prerogative which her son would one day expect to inherit. The king and queen failed to measure the forces which had caused the Revolution. They ascribed all their misfortunes to the work of a malignant faction, and believed that, if they could escape from Paris, a display of force by Bourbon-friendly powers would enable them to restore the supremacy of the crown... Maintaining seemingly innocuous conduct to the last, and trusting very few with their secret plans, on the evening of June 20, 1791 the royal family left the Tuileries, one by one, in disguise. A carriage awaited them on the Boulevard to take them on the road to Châlons and Montmedy. Louis left behind him a declaration complaining of the treatment which he had received and revoking his assent to all measures which had been laid before him while under restraint... The king had the bad luck to be sighted, recognised, and arrested at Varennes late on the 21st. National Guards seized him; other troops on the scene did not oppose them ... and the royal family [were sent] back toward Paris under guard.... From this point forward, the possibility not only of the deposition or forced abdication of this particular king but of the establishment of a republic entered the political discourse. It was now no longer possible to pretend that the Revolution had been made with the free consent of the king. Some Republicans called for his deposition, others for his trial for alleged treason and intended defection to the enemies of the French people. Mutual distrust between the Royalists and the revolutionaries deteriorated from this point, ultimately resulting in the guillotining of Louis (January 21, 1793) and of Marie Antoinette (October 16, 1793).