Greater Netherlandism was and is a macronationalistic trend affecting the present-day Kingdom of the Netherlands and the Netherlandic-speaking (Flemish) community of Belgium.

Germanic dialects spoken in the 15th/16th-century Burgundian Low Countries form a linguistic cluster called “Nether-German” by early humanists (with a floating demarcation from the Low-German dialects of northern Germany). When, in the late 16th century, the Burgundian lands fissioned, that language came to be referred to as “Dutch”  in the context of the Northern Netherlands and United Provinces (“Holland”), and as “Flemish” in the context of the Southern (Spanish, later Austrian Netherlands). The two halves of the language area were briefly united, politically, in the United Kingdom of the Netherlands of 1815, which also included a substantial French-speaking population in the “Walloon” South. The Francophones of the Southern Netherlands, notably in the erstwhile Prince-Bishopric of Liège and among Brussels liberals, were opposed to the dirigistic pro-Netherlandic language policies pursued by Willem’s high-handed government; riots broke out in Brussels in 1830, and the United Kingdom came to an end with the Belgian secession. While a political union between the Netherlands (“Holland”) and Belgium had proved unworkable, given the considerable social, religious and cultural differences, and especially the fact that half of Belgium was Francophone, the linguistic unity between the Netherlands and Belgium’s northern, Flemish-speaking half continued to inspire a sense of community and solidarity. (This Dutch-Flemish cultural convergence was resisted, all the same, by the Catholic West-Flemish “particularists” who saw their language and culture as altogether different from that of Holland).

Dutch-Flemish solidarity re-emerged in the 1840s, when the dust of the Belgian Secession had settled, Flemish patriotism for the new Belgian state began to wane in the light of the hegemony of French in public affairs, and the Pan-Germanic tendencies in German nationalism, as manifested in the irredentism over Schleswig-Holstein, began to inspire unease. Joint congresses of Flemish and Dutch philologists and medievalists were held on a regular basis from 1849 onwards, alternatingly north and south of the Dutch-Belgian border; orthographies were kept to a joint standard (against the wishes of the West-Flemish particularists), and a large common Dictionary of the Netherlandic language was undertaken. In addition, a neologism took root in the 1850s to describe the unity of the Netherlandic language as distinct from German and excluding Walloon/French: Diets – a semantic counterpart and antonym to its etymological cognate Duits (“German”). The term Diets was used in particular to refer to medieval forms and expressions of the language, and to a modern ideal of Flemish-Dutch community, thus in the review launched by J.A. Alberdingk Thijm, Dietsche Warande (“The Netherlandic garden”, 1855).

This cultural and philological concept began to inspire political solidarity by the late 19th century. There was substantial sympathy in Holland for the emerging Flemish Movement, which, as conflicts over language emancipation hardened in the period 1890-1920, came to develop an extreme political wing favouring the break-up of Belgium. In addition, a sense of solidarity with the Boers of South Africa in their resistance against British imperial power fed the ideology of a “Netherlandic race” dispersed over, and beleaguered in, different states. A possible political union of Flanders and Holland (in effect re-constituting the United Netherlands of late-medieval Burgundy and of the period 1815-1830, but excluding the Francophone territories) gained currency as a political ideal, widely among radical Flemish activists and more specifically, in the Netherlands, in circles around the Algemeen Nederlands Verbond (ANV, “Pan-Netherlandic Union”, founded in 1895). In the wake of the Boer Wars, Greater Netherlandism also propagated cultural and ethnic solidarity with “Afrikaner” settlers in southern Africa. Respected intellectuals like the historian Pieter Geyl endorsed the idea of Pan-Netherlandic unity; however, in the 1930s the Pan-Netherlandic ideal drifted increasingly from the conservative into the extreme right.

During the Nazi occupations the Diets ideology was carried exclusively by those Dutch and Flemish Fascists and Nazi collaborators who wished to maintain a certain particular status for Holland/Flanders within the Third Reich. As a result the Pan-Netherlandic ideology lost most of its public appeal after 1945, although the ANV maintained its existence and a number of fresh Dutch-Flemish associations were founded (with their main support in Belgium and in the Catholic parts of the Netherlands). Officially, the joint orthography and other general linguistic-cultural matters are a matter of institutionalized coordination between the Dutch and Flemish authorities; and speculations about the possible break-up of Belgium occasionally still inspire “what-if” scenarios in certain circles about a Flemish-Dutch union, demonstrating the long afterlife and latent background persistence of unrealized ideologies.