Random question

I'm not astonishingly good at keeping track of complicated human situations. Unless it's very well done (Game of Thrones, but *not* the sequels or the tv shows), I forget who's related to who and what the backstory was.

Obviously, there are people who are much better at such things than I am, but are there any real world events which went wrong because someone in charge simply forgot the details of alliances and enmities?

Two relevant links:

Not very funny, possibly could be improved with dotted lines:
http://www.washingtonpost.com/blogs/worldviews/wp/2013/08/26/the-middle-east-explained-in-one-sort-of-terrifying-chart/

Funny:
http://www.hyperorg.com/blogger/2013/08/23/game-of-thrones-season-4-episode1-no-spoilers/

Links thanks to andrewducker