The Attack on Amsterdam in July 1650 was part of a planned coup d'état by stadtholder William II, Prince of Orange to break the power of the regenten in the Dutch Republic, especially the County of Holland.

The coup failed, because the army of the Frisian stadtholder William Frederick, Prince of Nassau-Dietz got lost on the way to Amsterdam in the rainy night of 29 to 30 July.

Early 1649, the army still consisted of 35,000 mercenaries, and Holland (especially the dominant city of Amsterdam under burgomaster Andries Bicker) wanted to reduce their number to 26,000.

William II, however, was keen on leading a punitive expedition to England, where his father-in-law, king Charles I, had been decapitated on 30 January 1649, and the republic had been proclaimed; whilst the States of Holland urged to reduce the number of troops even further.

[1] He wanted to execute his plans in the spring of 1650, stemming from his astrological belief that the position of the Moon, Mars and Saturn would be favourable for a change of government, but eventually he would not act until summer.

[1] In May 1650, the States of Holland decided with 11 votes to 8 to disband the troops, and henceforth refused to pay part of the remaining soldiers' salary.

Morally supported by the States General, William II first decided to appoint a commission (with himself as its chairman) that would visit the cities of Holland to plead for a large army, but without success.

The latter and former burgemeester Andries Bicker rallied the city guard, hired 2,000 mercenaries, lifted the bridges, closed the gates and positioned the artillery.

The delegates from Haarlem, Delft, Hoorn, Medemblik, and Dordrecht (Jacob de Witt), were abducted under a strict guard to Loevestein Castle, some accompanied by their servants or their sons.

[4] Shortly after on 14 November, princess-widow Mary Henrietta Stuart gave birth to a son, the later king-stadtholder William III.