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Isabella the She Wolf was the daughter of a French King, and married the English King Edward II. Then came Ed III. Then his kids, Richard II and John of Gaunt. Richard II was King for awhile, but he was party-hearty, and he also stole all of Gaunt's lands. So Gaunt's son, Henry Bolingbroke (who Richard had banished) came roaring back to town, with some allies, and dethroned Richard, and then had his murdered. Bol became Henry IV. Then Henry's allies weren't too pleased with him, so he had to kick their asses--Mortimer, Glendower, Hotspur, Hot's dad, Hot's uncle, York and Douglas. And then Bol dies and his son becomes Henry V, and decides to take on the French (whose throne he claims through the She Wolf), but only after cutting one of his best friends, and hanging another for treason.
Once you translate this into a modern setting, it gets even more confusing, cause you can't have modern day people running around killing each other over throne succession.