It seems like in the Han-Xiongnu war, the Han were generally able to defeat the Xiongnu in a series of massive battles.
Was there anything about Xiongnu society that precluded their taking the traditional nomadic "Idanthyrsus strategy" against the Han invaders (avoid battle, poison wells, burn food stores, and keep distance until the invaders have to withdraw)? Did they have any major, immobile cities that were their vassals that they felt compelled to defend or anything? Did they have some notion of honor or chivalry that regarded withdrawal as disgraceful?
Or am I overestimating the frequency of pitched battles in the Han-Xiongnu war, and not taking into account how long the war was?
The Xiongnu did not willingly fight pitched battles, for the most part the did not, and in fighting against stepp nomades the best generals are those that manage to bring them to battle and defeat them.
There is a common pattern how stepp people can be defeated. Huge scale encirclment is the name of the game, just like in WW2. You had to put the stepp nomades into a fight, and then with very good tacitcs you can manage to beat them some of the time.
One must understand that the destruction of the Xiongnu was a MAJOR military effort for the Han dynasty that had more resouces and people and all that kind of stuff.