This study offers a theory in which nationalism is not only conducive to war -which is the conventional wisdom-, but also brings peace to entire groupings of states under a specific set of conditions. After the theory is laid out, a plausibility probe of 19th century Europe offers good justification for a continued research program of nationalism-as-technology and its effects.
The theory's insight comes from seeing nationalism not as an ideology, but as a form of military technology. For such technologies, their effect on war depends on how widely all countries employ them. When everyone has the same technology (i.e. when all countries are similarly endowed with nationalism), peace is cemented because countries mutually deter each other from launching wars of conquest. They do this by building mass armies to offset that of their neighbors, and threaten would-be conquerors with costly guerrilla wars and insurgencies. (Conversely, if only a few states possess the technology, the temptation to abuse it in conflict does rise.) The theoretical section of this study first justifies this analytical possibility of seeing nationalism as a technology. Among other things, the absence of definitional stumbling blocks is discussed. That is, given how technology is broadly defined by leading technologists, there is nothing inherent in the concept of nationalism that prevents its consideration as a technology. The study then proceeds to derive a series of hypotheses about the curvilinear effects of nationalism on war across a given region.
As mentioned, the primary case study is 19th century Europe (1815-1914), which lends itself to a plausibility probe. The results are corroborating. Napoleonic France first "discovered" nationalism as a technology with military applications - it formed the first mass armies and attempted continental conquest. Later on, other "early-adopters" also employed nationalism to take land from their neighbors. Sardinia, for instance, used Italian nationalism to build volunteer armies and fight Austria for control of northern Italy in 1859. But the early adopters were then followed by most other European countries, which took reins of their own nationalisms to build mass-armies and boost their defenses. In line with the theory, the widespread adoption of nationalism preceded two whole generations of European peace, from 1871 to 1914. (So rare was this long peace that it would not be equaled until after World War II.) In sum, the history of the 1800s seems to fit broadly with the theory, and gives good reason for continued research into the pacifying role of nationalism