I bought this book with some trepidation, because although I've read a fair few of Poul Anderson now, for me he can be very hit and miss, and things I like the sound of on paper I can end up hating.
Happy to say, Winter of the World ticks all the boxes for me. Set in the far future after our civilisation has been destroyed by a new Ice Age, a new empire from the south wants to spread into the northern heartlands of a group of 'primitive' tribes.
It is a short book, and Poul Anderson does throw a lot at you. But part of the enjoyment for me was reading between the lines, figuring out who the people he refers to relate to our world, and how history developed after our civilisation fell.
I am a fan of both Swords and Planet and post-apocalyptic stories - Winter of the World has elements of both, while also creating a fascinating society for the northern 'kiths'.
Glad I got it