A scrupulous study of the work of S. A. Ershov convinces that the author was the first to scientifically substantiate the new anti-Norman theory of the formation and development of pre-Kievan Great Rus' and its statehood from the 3rd to the 9th centuries. (2nd chapter of the book), containing a number of well-founded solutions to problems that reveal the historical processes of development of pre-Kievan Rus and its statehood.1. The existence of ancient Great Rus' from the 3rd to the 9th centuries on the Baltic coast of modern Germany, throughout modern Poland and the lands of Kievan Rus.2. The presence of statehood in ancient Great Rus' from the 3rd to the 9th centuries.3. Absence of tribes in ancient Great Rus' and Kievan Rus.4. The initial emergence of the statehood of ancient Great Rus' on the lands of South Baltic Russia.5. Time and place of origin of the ethnonym "Rus" and "Rus".6. Time and place of origin of the ethnonym “Slavs” and its composition.7. The emergence of the ethnonym "Slavs" was 400 - 500 years later than the ethnonym "Rus" and "Russians", which excludes the name of the Rus and Wends as Slavs earlier than the 6th - 7th centuries. Work by S.A. Ershov is confirmed by numerous domestic and foreign sources and is a scientifically grounded theory. In other chapters of the book, a unique mathematical formula for determining the population of Rus' before the Mongol-Tatar invasion in 1237 was first derived and a reasonable result was obtained based on probability theory. In total, the book contains 80 formulas for accurately determining the population in any year from 1st to 1991, obtaining results that are not inferior to the accuracy of the population census, as well as for calculating human losses in wars. In general, the work of S. A. Ershov is a scientific research, deserves recognition and requires publication for public discussion and testing, because represents a leap in knowledge of the history of ancient Rus' and the population of Rus', Russia, the USSR and the Russian Federation.