The play is about Joan of Arc, but it is also an allegory for political issues with which Shaw was concerned in the 1920s. One place where the allegory is evident is in Scene 4, when Cauchon describes the danger of Joan's "nationalism" to the Catholic Church:
To her the French-speaking people are what the Holy Scriptures describe as a nation. Call this side of her heresy Nationalism if you will: I can find you no better name for it. I can only tell you that it is essentially anti-Catholic and anti-Christian; for the Catholic Church knows only one realm, and that is the realm of Christ’s kingdom. Divide that kingdom into nations, and you dethrone Christ. Dethrone Christ, and who will stand between our throats and the sword? The world will perish in a welter of war.
Nationalism as we know it today coalesced as a political ideology at the end of the 18th century, with the French and American Revolutions, long after the time when the play is set. It saw a major resurgence during the years between World War I and World War II, when Shaw was writing this play. Shaw belonged to the progressive movement, which looked different in the 1920s than it does today. For instance, eugenics was part of progressive ideology in this time period before the Holocaust, a fact modern progressives are only beginning to grapple with today. Shaw believed in eugenics, and he believed in nationalism. Although it is difficult to understand today given the events of the past century, he saw both as crucial steps toward creating a utopian society with universal socialism. His logic was that a strong, unified state filled with "supermen" could provide everyone with the resources and legislation for them to thrive.
Shaw was especially concerned that the separation of Ireland into Northern Ireland and the Republic of Ireland in 1921 was a move in the wrong direction. He did not believe that Ireland needed to rule itself, but he did believe it needed to resolve its issues with England and become a strong state in order for Irish people to pursue other, more socially-relevant causes. Once again, he believed a strong nation-state could give rise to a socialist utopia. The conflict with England and the division of Ireland into an independent state in the south and a constituent country of Britain in the north had largely to do with religious tension between Catholics and Protestants. Cauchon's concern about Joan's nationalism stands in for the idea that religious identity should drive political divisions. Cauchon is worried that Joan's so-called "nationalism" will make the Church less powerful, just as Warwick is concerned that it will make feudal lords less powerful. Shaw represents both men as self-serving. Meanwhile, he presents Joan's "nationalism" and insistence that France should stay together as the driving force behind France's victory in the war. For Shaw, Joan's success stands in for the promise of a united Ireland.
