The Year of the Horsetails by R. F. Tapsell

The nomad warrior Bardiya must flee from the evil empire of the Mongol-like Tugars and their ruthless Kagan. He receives hospitality from the sedentary Slavic Drevich people; but fears that they also might succumb to the might of the Tugar empire. Will he be able to convince them of their danger and teach them the skills necessary to defeat their new enemy?
> This book was first published in 1967 by Hutchison & Co., and
> has been out of print until now.