Were the actions of the 3rd Duke of Alba in the 16th Century considered a Catholic Crusade? Fernando Álvarez de Toledo, 3rd Duke of Alba was sent by Philip II of Spain to Belgium where he waged war against the protestants in the area.

As a bit of history, Belgium in the 16th Century started out as part of the "Seventeen Provinces" within the Burgundian Netherlands.  Belgium was formed after the Eighty Years' War (1568–1648)

On February 16, 1568, the entire population of the Netherlands—three million—was condemned to death as heretics, apart from a few named exceptions:


  Philip next submitted a "Memorial and Representation" of the state of the Low Countries to the Spanish Inquisition craving the judgment of the Fathers upon it. After deliberating, the inquisitors pronounced their decision on the 16th of February, 1568. It was to the effect that, "with the exception of a select list of names which had been handed to them, all the inhabitants of the Netherlands were heretics or abettors of heresy, and so had been guilty of the crime of high treason." On the 26th of the same month, Philip confirmed this sentence by a proclamation, in which he commanded the decree to be carried into immediate execution, without favour or respect of persons. The King of Spain actually passed sentence of death upon a whole nation. We behold him erecting a common scaffold for its execution, and digging one vast grave for all the men, and women, and children of the Low Countries. "Since the beginning of the world," says Brandt, "men have not seen or heard any parallel to this horrible sentence. (Wylie, History of Protestantism, vol. II, p. 70.)


Would the sending of the 3rd Duke of Alba to Belgium and his following actions be considered a Catholic Crusade?
Professor Petrus Johannes Blok was Professor of Dutch History at Leiden University, the Netherlands oldest university, in the late 19th and early 20th century. In 1907 he identified that the decree sentencing almost all Netherlands inhabitants to death, and depriving them of their property, said to have been promulgated in Spain in 1568, was actually a forgery dating from some time in the 1570s. In a sense then, it was, according to the Professor, fake news, but from the 16th century; and generally accepted by historians until the 20th. 

See page 42-43 of "Britain and the Netherlands Volume 5" by Bromley and Kossmann .

The Netherlands  Inquisition had been running for several decades already and, as Phillip II himself observed, was less merciful than the Spanish. At one time heretics who  refused to repent could be burned. If a man or boy repented he could be beheaded, but if a woman or girl repented she could be buried alive.

This article, on the website of St Andrew's University, the oldest in Scotland, quotes estimates of 50,000 to 100,00 deaths. After the Duke of Albi arrived many more thousands of deaths were inflicted, it says.

This was the same Duke of Albi who in 1556 had besieged Rome and threatened to sack the city if the then pope did not accept his terms.  

However no attempt was made to exterminate almost all the inhabitants of the Netherlands indiscriminately. The decree, even if it had existed, was not acted upon. That the Duke of Alba did lead a force to the Netherlands and that much persecution followed is true. 

The historical details are somewhat disputed and perhaps the History site might provide some answers  as to roughly how many perished, and how many suffered other punishment or went into exile.

If, in fact, the Pope had approved a campaign to kill all 3,00,000, many of whom were Catholic anyway, and had called on all Catholics to support it,  then that would have been a most extraordinary thing. We can only speculate whether it might have been called a crusade, or what it might have been called.

Rather depressingly, perhaps, what actually happened was, in the context of sixteenth century Europe,  more a case of "business as usual".