 In the 1920s, the period of initial studies of the Nanai language, the area of settlement of the Nanai people was more extensive than at present; many dialects, which had not yet been classified by researchers, later disappeared, and remain unnamed.The next period of studies did not begin until after a 20-year interruption, at the end of the 1940s; by then, the number of dialects had grown, and subsequent classifications distinguished as many as ten.Also, the distribution of the Nanai language had sharply narrowed; many Lower Amur and Ussuri dialects remained unstudied.