The article is devoted to the history of Eastern European irregular troops, widely spread in Russia, in the Polish–Lithuanian Commonwealth and in the Habsburg possessions in the XVI–XVII century. It substantiates the position that all such troops, in particular, the Cossacks, Grenz infantry and lancers, was a single phenomenon, and to understand some of the peculiarities of their evolution should consider their history comprehensively. Based on the approaches proposed by F. Mehring, the article concludes that the proliferation of irregular parts in the Christian Eastern Europe was the result of specific socio-political conditions, especially long wars and borders of the Asian type. In these circumstances, governments were created or were invited to the service of paramilitary units, instead of receiving wages various benefits. The result is a system of irregular troops, the geographical scope of which was limited to the Adriatic sea and the Urals.