Since the middle of the 19th century when the research of the comparative school began, it had established the close connections between the mythologies of various Indo-European peoples. The Slavic system appeared to be kindred to the Greek, Roman and Indian systems. The entire pantheon began to be thought of as derived from the common matrix of the original Indo- European ethnos (Ur-Volk). In the spirit of the solar-mythological school, the anthropomorphic deities were thought of as derived from the worship of nature, and through poetic allegories (see D. O. Shepping, A. N. Afanasyev). In the spirit of diffusionism, A. S. Famintsyn continued the Slavophile traditon, while N. I. Kareev defended the secondary emergence of monotheism. The adherents of evolutionism, developed in the 70s and 80s of the 19th century, derived the images of gods from the lower demonology — from the belief in spirits (in Russia demonology was studied by N. F. Sumtsov).
The evolutionist and diffusionist approaches were combined in the works of Lubor Niederle and A. N. Veselovsky. Both of them thought that the Slavs did not succeed in developing a higher mythology and had remained on the level of demonology. Other scholars rejected the conclusions of the mythological school for a different reason. They stressed the shortage of available facts and did not believe in the reliability of any of the offered hypotheses (W. Jagič, H. Máchal, L. Leger, A. Kirpichnikov).
In the works by scholars of the 20th century (E. V. Anichkov, N. M. Galkovsky, V. J. Mansikka), this scepticism was overcome, and the analysis of sermons by orthodox preachers against survivals of paganism came to the fore. But following the preachers' vilification of the pagan practices, the scholars involuntarily inherited their bias as well. They still viewed paganism as a rough and primitive belief system. Anichkov, for instance, held that Rus abounded in minor gods (or rather demons) while the powerful major gods were borrowed from the Varangians. In this he followed S. Ruzhnetsky's work on Perun as an imitation of Thor.
In the 20th century, the Polish scholars (H. Lowmianski, W. Szafraňski, L. Moszyňski) picked up the trend emphasizing the primacy of attributes of monotheism in Slavic paganism. One may detect in this the influence of Catholicism. For these scholars, Perun was not simply the main god, but the only god, all others being only his incarnations.
Among Soviet scholars, the official militant atheism had prevented the study of Slavic paganism for a long time. Besides, their obligatory Marxist vitriol was reserved mainly for the major ideological enemies — Christianity and Islam. However not long before the Great Patriotic War (World War II), the interest in Slavic paganism was revived due to the regime's encouragement of patriotism in the country. Four new concepts of Slavic paganism were introduced. In all of them the focus had shifted from using historical records to those provided by ethnography and archaeology.