I've read very little about East Asian warfare, but I seem to recall that transient sieging was popular; you confirm the use of terror and civilian massacre. As for density, I don't know that there would have been a considerable difference between medieval Europe and medieval Japan in the ratio of coherent, nominally-independent political entities to land area. For instance, at the end of the European medieval period there were over 500 such 'state-units', including maybe a couple-dozen great powers (Charles Tilly, Coercion, Capital, and European States).

Visually:

Map of Japan at the beginning of the Tokugawa era (16th c.).

Map of Europe in 1477.

By the way, for a picture of the 'ritualized tribal warfare' I referenced, see Hans van Wees' essays on "The Homeric Way of War".