I know the basics - Henry inherits the Duchies of Normandy and Aquitaine and forges what some refer to as the Angevin Empire. But I've been reading some stuff on his reign and found what looks like some succession war for the Duchy of Normandy. Could you tell me how this war was fought and who against?
The Angevin Empire was much more a product of diplomacy and politics than it was about conquering or forging an Empire. In fact the idea of calling it an Empire is a more modern concept. English kings at the time we're really French nobility who happened to also hold the title of King of England. King Henry and his predecessors predominantly spoke French and typically held Court in their French holdings. Despite being a sovereign King in England Henry was still a vassal in France and subject to the king of France. So the Holdings that Henry and his house acquired we're not viewed as we see an Empire today, but more Through The Eyes of a vassal.
There are a few different ways in which a leader can acquire titles and holdings and for Henry these Holdings came in three different ways- either through inheritance, right by marriage, or by treaty. So first let's take a look at what exactly comprised the Empire. There was, of course, the Kingdom of England. By King Henry II's reign, England also controlled some territory in Ireland and had control in Whales, but I'm going to gloss over this as the main interest is in France.
The other holdings were duchies and counties of France, including the duchy or Normandy, the duchy of Aquitaine, and the counties of Anjou, maine, and Nantes.
Ever since William, Duke of Normandy, conquered England in 1066, the duchy of Normandy has been passed down to family and eventually made its way to Henry. Matilda, Henry's mother was this link to William, but he also inherited some titles from his father Geoffrey Plantagenet who had held both the county of Anjou as well as Maine.
Henry II eventually married Eleanor, the ex-wife of King Louis of France. Eleanor was the duchess of Aquitaine and through marriage this made Henry the Duke of Aquitaine.
Finally, we have Nantes, which was the county capital of Brittany. An uprising had erupted over leadership in the duchy and after Henry came in on the side of the opposition, a treaty was drawn up granting him the title of Count of Nantes. Henry eventually granted this title to his son who then, through marriage, brought the duchy of Brittany into the English house.
Sources: The Angelina Empire by John Gillingham,
Britain's Royal Families by Alison Weir.