Yeah, but a large part of Belgium still wasn't part of it, including Luxemburg, Liege, Limburg, Namur, Walloon Brabant, Flemish Brabant and Antwerp. Actually it was merely Flanders and Hainaut (and Holland and Zeeland). I would place the union the earliest around the time of Philip the good, but even than you lack the bishopric of Liege. I would say that the earliest foundation of Belgium lies in 1684 when it was split from the Netherlands, but even then it still lacked its own identity.That's very easy, 1384 is the official founding year of the Burgundian Empire you talk about.