What it says on the tin; what is the maximum territorial extent that a state situated in the Low Countries can get and how can it get there? Bonus points if you can have it hold most of its borders until the 20th century. Doesn't have to be the Netherlands/Dutch-led so long as it is based in the area, so a Belgiumwank and a Luxemburg wank would count too. As for PoD, I would push it as far back as even as the creation of Lotharingia/Middle Francia if you so choose.