Why is today the 1st of December a public holiday in Portugal?

Today, the Restoration of Independence in Portugal is celebrated.
This date recalls the action of Portuguese nobles, who on December 1, 1640 invaded the Royal Palace and killed Miguel de Vasconcelos, the representative of Spain in Lisbon, acclaiming D. João, Duke of Bragança, as king of Portugal.

The Restoration of Independence was the culmination of a period of great discontent on the part of the Portuguese population, discontented with the Iberian Union, between Portugal and Spain, which lasted for 60 years (from 1580 to 1640).
The Iberian Union caused problems for the Portuguese population, with tax burdens and Portugal´s involvement in the conflicts in Spain.
With the death of the young D. Sebastião in the battle of Alcácer-Quibir, Portugal faced a succession problem. After the failure of Cardinal D. Henrique in command of the monarchy, Portugal was ruled by three kings D. Filipes of Spain, for 60 years, a period that became known as Filipino Domain.

Restoration of Independence Day, December 1, is a national holiday. As of 2013, as part of a package of measures aimed at increasing productivity, the Portuguese government had decided to eliminate the December 1 holiday. However, the celebration of the Restoration of Portuguese Independence was resumed as a public holiday in 2016.

The Restoration of Independence, more precisely The Restoration of Portugal as a sovereign country, is the name given to the revolutionary coup d´état that took place on December 1, 1640, led by a group known as The Forty Conjurados and which spread throughout the entire kingdom, for the Portuguese revolt against the attempt to annul the independence of the Kingdom of Portugal through the governance of the Castilian Filipino dynasty. As it culminated with the establishment of the 4th Portuguese Dynasty – the house of Bragança – with the acclamation of D. João IV – it is also correctly designated as The Acclamation of the Independence of Portugal.

Source : O Emigrante : Mundo Português