Short answers, pulled from the story.
Belgium, Luxembourg, and the Netherlands form the core of the Low Countries. Parts of France such as Nord and Pas-de-Calais sometimes join the definition. German regions like East Frisia, Guelders, and Cleves also appear within its boundaries.
Charles V inherited Burgundian holdings in 1506 and was named ruler by the States General. He styled himself as Heer der Nederlanden and united territories into one indivisible entity called the Seventeen Provinces. The Pragmatic Sanction of 1549 streamlined succession laws so all provinces would pass to one heir.
The House of Valois became rulers of the Duchy of Burgundy and transformed the region into Northern Europe's cultural center. Cities like Bruges, Ghent, Mechelen, Leuven, Tournai, and Brussels flourished as hubs of Early Netherlandish painting. Musicians from the Franco-Flemish School were highly sought after across all European leading classes.
Germany's Blitzkrieg tactics overpowered defenses across Belgium, the Netherlands, and Luxembourg by May 1940. All three nations remained occupied from May 1940 to early 1945 while governments fled to Britain. In 1944, they signed the London Customs Convention laying foundations for the Benelux Economic Union.
The United Kingdom of the Netherlands existed between 1815 and 1830 before dividing into three modern countries. During World War I, Central Powers invaded Luxembourg and Belgium in what is now called the German invasion of Belgium. Approximately 56,000 people were killed during this initial phase of conflict.