While I do not disagree with the basic premise of the article, the history presented here leaves something to be desired. Charactarizing the period between 1815 and 1914 as one of “general peace” in Europe is, to put it politely, open to debate. They had:
The Crimean War, a war between Belgium and Holland, Portugal and Spain. There was a war between Poland and Russia, an Austro-Prussian war, A Danish war, a French expidition to Mexico, wars in Italy, colonial rebellions in India, a Russian Turkish war,and, the war that set up WWI; the French/German war of 1871. Etc., etc.
I suppose that if we look between the European wars of this time period, we can find short periods of “general peace”, but not many.
Compare 1815-1914 with the level of warfare seen from 1700-1815, with the Spanish War of Succession, Austrian War of Succession, French Revolution and Napoleonic Wars, the Great Northern War, the Anglo-Spanish War, the first Russo-Turkish War, the Second Russo-Turkish War, the Third Russo-Turkish War, the Seven Years' War, the Barbary Wars, the Finnish War, etc. Many of these were genuine world wars, fought all over the colonial world as well as across Europe, and many of these were long wars that lasted for several years.
In comparison, many of the wars you list in the 19th century were comparatively short (i.e. the Franco-Prussian War lasted 10 months, the Austro-Prussian War lasted seven weeks) or not really applicable to the historical point being made - for instance, the "Holland-Belgium" war you mention was actually the secession of Belgium from Holland, not really an international war, and consisted of one large battle, arbitration engineered by the British (in line with the point of that paragraph in the article), and then a ten-day period in which the Dutch tried to overturn arbitration before being persuaded to desist by the French. The colonial rebellions in India and the French expedition in Mexico are also outside the realm of the point being made since they didn't take place on the continent of Europe, which is what that section of the article was dealing with.