The wrangling between GM and Fiat

If I was a lawyer, I'm sure I would understand what the heck is going on between GM and Fiat. But I'm not, so I really don't. What I do know is that the two auto manufacturers are fighting over who will control Fiat's automobile unit. But, it's not exactly as it sounds. According to an agreement between the two companies from 2000, when GM bought a 20% share of Fiat Auto, Fiat could force GM to purchase all of Fiat Auto at a later point in time (sick of hearing Fiat yet?). Well, apparently, that later point in time has come, and Fiat, who is losing billions of euros annually, want to force GM to purchase the remainder of its auto unit. GM is none to happy about that prospect now, and is fighting it based on the fact that its share was reduced to 10% in 2003 by a capital increase (whatever that means). Either way, I want to know what GM was thinking when it agreed to this one? At what point in time did the idea of Fiat being able to force GM to purchase the rest of its auto group sound like a good idea to GM? I'm lost…