North and South Holland, two of eleven (now twelve)* provinces, have long been vastly richer and more-densely-populated than other areas of The Netherlands. They contain Amsterdam, the cultural and financial capital, The Hague, political capital, and Rotterdam, a major port at the mouth of the Rijn (Rhine) all of which are part of the Randstad, the Dutch ring-shaped megatropolis.
The Nieuwe Hollandse Waterlinie is "new" in relation to the original north-south defensive inundation zone, the "Oude Hollandse Waterlinie." The old system did not encompass Utrecht, the easternmost city in the Randstad, because at that time, in the late 1600's, Utrecht was under French rule.
After the fall of Napoleon in 1815 the Dutch began construction on the Nieuwe Hollandse Waterlinie, which entailed a shift eastward of the defensive line, and improvements in the technologies.