The 26 cantons that makeup Switzerland have always been religiously, linguistically and economically different. However, after 1848 (and after the Sonderbundskrieg of 1847) religion is no longer a matter of political dispute. The language borders are a serious dividing line, however, especially between the Romandie (six (mostly) French-speaking cantons in western Switzerland, and the (mostly) German-speaking cantons.
The First World War was a period of tension between these two regions. Various incidents were the direct cause (e.g. the appointment by the parliament of the German-speaking general Ulrich Wille (1848-1925) and espionage affairs).
The Romandie mainly sympathised with the Entente (France, England, Russia, Belgium), German-speaking Switzerland was mostly at the hand of Germany and Austria. The Sprachgraben was born, the ‘gap’ separating Romandie and German-speaking Switzerland. Only later would the Röstigraben become the term. (Rösti was ‘German-speaking’ food, mainly made of potatoes). The river Saane near Freiburg is often the (symbolic) dividing line. It also indicates the irony of history. Freiburg, now mainly French-speaking (Fribourg) was until the sixteenth century a German-speaking (catholic) canton. The German-speaking writer Carl Spitteler (1845-1925) was one of the calming voices in 1914, also from the Romandie came reconciling views. It is one of the reasons why it did not come to a rupture.
However, the General Strike of November 1918, born of discontent, poverty and impressed by the revolutions in other countries, brought reconciliation to the French and German-speaking elites. French-speaking soldiers from canton Vaud, for example, were deployed in German-speaking Grenchen (canton Solothurn) to break the strike. As a token of gratitude, the town gave des amis Vaudois a generous bonus.
However, the Röstigraben had not yet disappeared. That became clear when Switzerland joined the League of Nations in 1920. The German-speaking cantons and citizens were much less enthusiastic than the Romandie. The rejection of the EU in 1992 also ran along these lines, although the French-speaking citizens were (and are in 2020) also opposed to this EU in the second referendum in 2001. The UN accession in 2002 was also a repeat of 1920. At the beginning of the Second World War, however, both regions were united in their support for the Allies. The appointment of the French-speaking general Henri Guisan (1874-1960) certainly contributed to this.
Nowadays, the political dividing lines are no longer so much along the Röstigraben, but rather in a ‘gap’ between rural and urban areas in both regions. Globalisation also contributes to this development. It does not mean that there is no longer a ‘gap’. Switzerland is the connecting factor, and they are all Swiss. But language separates in mentality, culture and manners. By the way, the German and French-speaking cantons are not a unity either. The many German dialects (Schwyzertütsch)already point to this. The Röstigraben certainly still exists, but there seems to be (more) uniformity in many areas, partly due to the globalisation. Language as a means of expression and media, however, remains a sign of distinction. There is, however, no separation in present-day Switzerland. Rösti became popular in the Romandie after all.