The article examines the phenomenon of nationalism as such and its Eastern Christian variations. In particular, two main theories of nationalism are described: modern and pre-modern. There are also two stages of the development of nationalism: emancipatory and oppressive. The former is healthier than the latter. The article focuses on the Orthodox versions of nationalism that are consistent with the traditional structure of local churches. In the Orthodox world, national individuality in combination with church locality can be either ethnic or civilizational. The former strengthens a homogeneous national identity in the Balkan style. The latter is Orthodox neo-imperialism, which is incompatible with nation-building. Their incompatibility often leads to conflicts and even wars, as in the case of Russia’s war against Ukraine.