Yes firebrand, there was definitely nationalism involved but this was a doctrine that was only fully embraced by elites. Most common people in most parts of the world had absolutely no clue as to what the leaders of these empires were fighting for. In France, for example, there were once hundreds of different little townships culturally fragmented and without any conscious realization of a "French" identity. They only identified locally with the customs and traditions of the people around them. That was an example, but the same was true for the persians, the arabs, the many various regions of Africa, the land today known as india, the indians of the americas, etc. Only when you look at history through the lens of elites will you find nationalism and only today is nationalism a sentiment that exists en masse throughout any single nation-state. In fact, when capitalism emerged and the capitalist states established themselves, one of the greatest difficulties in most "countries" was developing a unified feeling of nationhood among all people with a set of borders. How can we have a market for wine, for example, when there are 30 or 40 different types of distinct wine throughout he land? Well, you develop propaganda to narrow what is considered good wine so that a few rich distributers can sell within larger markets. In fact, the whole public school system idea developed as a means, in the majority of nation-states, to unify the language (as most languages differ from region to region), develop national mythology about why "we are one nation of people" and basically condition people in accepting that they are all cultural the same and especially different from their nation-state neighbors (hence competition).