Well I voted:

Monarchic Dynasties (first) - dynastical mariages were not rare among thoose kingdoms. Ptolamaid/ Seleukid Mariege, the Maiage between the Hay and Pontic royal families.

Another Monarchis Faction (second) - as much as I know then marriages between "leading families" of different tribes was not uncommen aswell (I'm not sure however, maybe the EB team knows more).

Nomadic tribals - I voted on this because Marriage was often seen as a form of "uniting", "merging" two tribes since the child would descend from the Ancestors of both "dynasties" and would have a divine right to rule both (however this custom did change from tribe to tribe and era to era so I still consider it uncertain). The other point for it was that in several cases in history "settled dynasties" often married with nomadic warlord families (and the other way around) to secure alliances/military support.