The Importance of Love in History

I have heard before that some the greatest fallen leaders of history owe their fall to a girl. When I first heard this, I couldn't find the logic in the statement. It has taken me a few years to begin to understand what this means. At first glance I thought it meant some great leaders had evil wives who wanted nothing more than to see their husbands fail (by "great" I am referring to their impact in the world whether positive or negative, but I, in no way, shape or form condone their actions or beliefs); however, after a few years of letting that statement simmer on the back-burner and having gone through a few life lessons myself, I came to realize that this statement would be more accurate if it read as follows:

Some of the greatest fallen leaders of history fell in love.

I don't think it had much to do with their significant other or their significant other's psychological state. I believe these leaders fell in love and did some crazy things BECAUSE they were in love. I am setting out to see the importance of love in history and what role it played in key moments. Could certain things have gone differently if John F. Kennedy never met Marylin? Or maybe Hitler never meets Eva... what kind of world would THAT have been?