Just a couple of little points.

from Takio
Close, he actually used the example of Tartar tribes as transnatinal non-sate actors.
Depends on how you translate the Tartar passage from Bk 8.3B:

Die Tatarenschwärme suchen neue Wohnsitze. Sie ziehen mit dem ganzen Volke aus, mit Weib und Kind, sie sind also zahlreich wie verhältnismäßig kein anderes Heer, und ihr Ziel ist Unterwerfung oder Vertreibung des Gegners. Sie würden mit diesen Mitteln bald alles vor sich niederwerfen, ließe sich damit ein hoher Kulturzustand vereinigen.
I'd translate "dem ganzen Volke" as "their entire Nation"; and "Die Tatarenschwärme" as the "The Tartarhordes" (literally, it's "The Tartarswarms"; but the later Tartar political entities usually are called "Hordes" - e.g., the "Golden Horde").

I may be influenced by reading Gabriel's bio of Subotai. The historical facts are that when the Tartars "ziehened aus", they were very much a nation-state (with geographic bounds as they chose to define them; and a clear governance structure). They also a very organized military structure (part and parcel of their government). So, legally, I'd class them as a nation-state (albeit living in tents); and their soldiers as regular combatants (brutal, but regular).

The Germanic tribes who crossed into the Roman Empire seem more akin to Transnational Violent Non-State Actors - not nation-states; and their troops more akin to irregular combatants. Which period of German history you pick makes a difference. The Germanic groups named by Tacitus (ca. 100ce) had defined boundaries, a governance structure, etc. By 400ce, that had been disrupted by pressure from the East, resulting in the Rhine Crossing, etc.

I think Wilf is more factually on point with this:

from Wilf
CvC was very aware of the Catholic and Protestant "insurgencies" and Wars within Europe, including the Hussites. These are all basically "trans-national" or "non-state".
Agreed factually - and good examples of pre-Westphalian non-state actors in armed conflicts. However, did CvC discuss them ? I did a search through the On War I downloaded (Graham trans.); and had no hits for Catholic, Protestant, Hussite or religious. Anyway, if someone could supply a CvC reference to those armed conflicts, if it exists ?