Short answers, pulled from the story.
The Seventeen Provinces were the Spanish Netherlands before the Dutch Revolt, covering most of what is now the Netherlands, Belgium, Luxembourg, and parts of northern France. The territory was known in three languages: Zeventien Provinciën in Dutch, Dix-Sept Provinces in French, and Diecisiete Provincias in Spanish.
The Seventeen Provinces passed to the House of Habsburg in 1482, following the death of Mary I of Valois, Duchess of Burgundy. From 1556, they were held specifically by Habsburg Spain.
The Pragmatic Sanction of 1549 listed only fifteen provinces, not seventeen. Scholars believe the total of seventeen came from counting Zutphen and Groningen as separate provinces rather than as parts of larger units. Some sources attribute the number to Christian symbolism rather than a precise territorial count.
The Eighty Years' War began in 1568 and ended with seven northern provinces forming the Seven United Provinces in 1581. The southern provinces, including Flanders, Brabant, Namur, Hainaut, and Luxembourg, were restored to Spanish rule through the military campaigns of the Duke of Parma, culminating in the Siege of Antwerp in 1584-1585.
The Sack of Antwerp in 1576 and the subsequent closure of the Scheldt river to navigation ended Antwerp's position as the economic centre of the Netherlands. Large numbers of people from the southern provinces emigrated northward, shifting prosperity from Bruges, Antwerp, Ghent, and Brussels to Amsterdam, The Hague, and Rotterdam.
The County of Flanders historically covered roughly what are now West Flanders, East Flanders, and French Flanders. In the 19th century, the name Flanders was applied to the Dutch-speaking part of Belgium as a whole, a larger territory that contains only part of the original county. French Flanders, for example, was part of the historic county but now belongs to France.