Nationalism was beneficial to 19th and 20th century Europeans.

From dictionary.com nation - a large number of people who share the same history, ancestors, culture etc (whether or not they all live in the same country) This is the historic meaning of a "nation" which I am using for the purpose of this debate. I will first address your points. A. It encouraged unification at the cost of the lives of other ethnic groups, hardly something to be proud of. B. The growth of states and economies are attributed more to other things (will explain later). C. Nationalism swept through Europe after the French Revolution, which occurred during the Enlightenment, which was a time of intellectual flowering, not a dark age. D. States were already well consolidated, and could handle their subjects. The concept of divine right, already dying out, had strengthened kings at the expense of nobles and feudalism. Constitutional government and Parliaments were being set up in the 1800s as a result of classical Liberalism, which was often in direct conflict with nationalism. As well, economies were doing fantastic prior to the onset of nationalism. Britain, with a massive colonial empire (and plentiful natural resources, a liberal government, etc), was in the middle of a massive economic change, the Industrial Revolution. This would soon spread to the continent, well before the savage onset of nationalism. The first IR started in the 1750s, and went until the mid 1800s, starting well before nationalism became a real force. E. Nationalism was a political tool used by leaders to gain power, fooling people into thinking it was for their own good. For instance, nationalism allowed for German Unification in 1871, a byproduct of Bismarck's wily diplomatic moves. However, the old king of Prussia became the new king of Germany, and although the Reichstag was established, it had virtually no power (it could not originate laws, ministers appointed by king, heavily influenced by Bismarck and the Kaiser, etc). In fact, nationalism often allowed for the creation of new, more powerful, and thus, more oppressive monarchies. The creator of these democratic governments was actually classical Liberalism. F. Ultimately it was not nationalism that destroyed kingdoms, but the constant pressures of liberals. The conservative order attempted to stay in power using nationalism (see Bismarck, Cavour (Piedmont PM)). G. The Frankfurt Parliament gave a chance to the Prussian king to rule Germany as a constitutional monarch, well before unification occurred. Liberalism would have created a united Germany, one with a weakened monarchy which would be unable to turn to militarism. Instead, the Prussian king refused, and a few decades later, under the guise of nationalism, Prussia was the master of Germany. In effect, the reason that there were such militaristic governments was a byproduct of nationalism. This militarism is what lead to new imperialism, so nationalism is closely linked. H. It is true that imperialism/militarism were factors in WWI, but both were byproducts of nationalist governments. The alliance system also would not have caused war if it were not for nationalism. Serbians seeking to gain territory at Austria-Hungary's expense, and members of a secret society collaborated together to kill the Austrian heir to the throne. This was the spark plug, nationalism, for the war. As well, the conditions prior to the war were because of nationalism, so we have an indirect and direct link to nationalism. I. Facism involved nationalism. It is about returning one's nation to its glory days. Hitler and Mussolini both sought to take lands that they felt were those of their nation. Hitler wanted the lands Germany had lost in war, and much more. There were also several provinces outside of Italy which had not yet been taken yet, driving Mussolini. Furthermore, some of the most horrific parts of WWII, such as the Holocaust, were direct products of nationalism. Jews were considered to be a different nation by Germans (see the real definition of a nation above), and thus, the government tried to eliminate them, along with others who they felt were not real Germans. J. It does not matter if nationalistic revolutions were coming to an end by WWII (though do see the Balkans), nationalism is not simply about revolutions, it is an outlook. K. The US is the "hub" of classical liberalism. From the right to property and free speech, constitutional democratic government, religious toleration, laissez-faire, all of these traditional elements of the US government were products of classical Liberalism and the Enlightenment. In fact, the US is not even a nation by the historical definition of the word, but rather a group of nations in a single unified state. Because we do not have a homogenous culture, a homogenous ancestry, etc., we are not a "historic nation". L. Finally, what the US is or is not is not even truly consequential to this debate, because this is about EUROPE! Clarifications on Liberalism and Nationalism Nationalism is the feeling of superiority of one's culture. It is the belief that you all all those in your "nation" deserve a state. It is the notion that your people are destined to rule some piece of land, and that your people are better than everyone else. In a nationalistic state, minorities are often persecuted. Classical Liberalism on the other hand is the product of the Enlightenment. It is about laissez-faire, personal liberties, religious toleration, constitutional/democratic government, rights for minorities, etc. Continuing my Arguments Nationalism lead to WWI and WWII. It also directly lead to the Holocaust, therefore, the deaths of so many. Nationalism was an unruly ideology seeking to challenge the status quo of Europe, to challenge the general peace that had lasted for half a century. For instance, in the Austrian Empire, constant Magyar irritation lead to the creation of the dual monarchy (Austria-Hungary, each area has its own king). The Magyars then consolidated rule of their land and persecuted the many nationalities within their borders (Poles, Slavs, Germans, etc.). This is hardly an isolated incident, in fact, nationalist groups often sought independence for their nation while denying the independence of other nationalist groups. This lead to much death and persecution. As well, the general revolts and numerous wars (Austro-Italy, Austro-Prussia, Franco-Prussia) caused by nationalism achieved little good for Europe at the expense of many lives. Overall, nationalism made peace more difficult to achieve and lead to countless deaths. Nationalism is bonded in history, bonded to WWI, WWII, the Holocaust, pogroms (government riots against Jews) in Russia, the persecution and impostition of Russian culture on Poles, and so many other atrocities. What good that occurred during the rising of nationalism only occurred because liberalism was not crushed by it. One of the few things these movements had in common was that they were foes of the old order. Ultimately, one (classic Liberalism) was a force for good, for change, for better economies, for better science, for better sanitation, for better cities, for better lives. And the other was the tool of fanatic scoundrels and power-hungry politicians. And so nationalism, in the historic sense, was a calamity for 19th and 20th century Europeans.