Avalon Hill, 1976, 2-6 players, ages 12 and up. I haven't actually tried out this game - the people in my gaming group refuse to have anything to do with it. Apparently it's just not all that good, and shares too much in common with another game that we do play a lot - Games Workshop's Warrior Knights.
Anyway, here's what BOARDGAMEGEEK.COM has to say about it:
"Kingmaker is based on the War of the Roses in English history, a time of civil war when two royal houses competed for the rightful throne. Players control factions using their military and political power to control and influence the royal heirs, supporting the heir in their control as king while trying to take down all of the other heirs."