But these periods of greatness were short-lived compared with the periods of decadence which succeeded them. After the division of the Empire of Charlemagne the Belgian counties and duchies found themselves plunged in the throes of feudal disputes and divided between the Kings of France and the Emperors of Germany. The power of the suzerain was nowhere weaker than in these distant marches, and the Belgian princes were left free to pursue their quarrels with complete disregard of the common interest. The prosperity of the Communes in the thirteenth and beginning of the fourteenth centuries, was rapidly undermined by internal strife and by the difficulties the Counts of Flanders experienced in trying to conciliate their duty to their French suzerain with the interest of the people which prompted an English alliance. The fall of Charles the Bold provoked a fresh outburst of the spirit of local independence, which greatly endangered the country's peace, and, if the situation was restored, under Philip the Fair and Charles V, during the first part of the sixteenth century, the second part of this century witnessed the gradual exhaustion of the Southern Netherlands divided against themselves and subjected to the attacks of both Spanish and Dutch.
The seventeenth and eighteenth centuries, which are for other countries, like France, a period of exceptional national prestige, mark the deepest stage of Belgian decadence and humiliation. The Scheldt was closed, trade and industry were practically dead, foreign troops, French, Dutch, Spanish or Austrian, ceaselessly pursued their work of devastation. A foreign possession, open to the incursions of her possessors' enemies, sacrificed by her masters at every stage of the peace negotiations in order to save their native country, Belgium lost Dutch Flanders, Northern Brabant and part of Limburg to Holland, French Flanders, Franche Comté and Artois to France. The Treaty of Münster sealed the fate of Antwerp, and the Treaty of the Barriers left the Dutch in possession of all the country's most important fortified positions.
Though it gave back to Belgium her natural frontier in the North and reopened the Scheldt for a short time, the French régime did not greatly improve the economic situation. After the union with Holland (1815), the political struggle which followed prevented the people from enjoying the full benefit of the change, so that we must wait until 1830 before being able to notice any considerable improvement.