I suspect he was referring to

https://en.wikipedia.org/wiki/Polder_model#Historical_backgr...

Interesting read. Quote:

> Ever since the Middle Ages, when the process of land reclamation began, different societies living in the same polder have been forced to cooperate because without unanimous agreement on shared responsibility for maintenance of the dykes and pumping stations, the polders would have flooded and everyone would have suffered. Crucially, even when different cities in the same polder were at war, they still had to cooperate in this respect. This is thought to have taught the Dutch to set aside differences for a greater purpose.

Yep, that one