A meeting at The Hague last week, Premiers of the three Benelux nations looked back on eleven years’ experience of union, and found it good.

Back in 1946, in a historic meeting at The Hague, the leaders of Belgium, The Netherlands and Luxembourg committed their nations to a far-reaching experiment in cooperation and trust among Europe’s sovereign states—an economic union that obliterated economic borders to let goods, capital and labor flow as freely as…