They were over a rabbit. They both wanted the place to be leader. So they ended up fighting each other for leader ship and because of the rabbit.
Buck arrives at Klondike
Curly wasn't able to survive the fight or she wasn't able to adapt in surviving very long with all the challenges they had for them to survive.
Buck finally defeated Spitz. From all this time they have been fighting for leadership Buck finally got the place he deserved and worked hard for.
Buck finally arrived to Klondike. But when he got there they treated him badly again and Buck stayed strong and took on the consequences that him or any other dog deserved.
Buck keeps having dreams of cave man because Buck notices how far he has come to be where his at in leadership and loyalty. Buck also has dreams of cave man because he see for himslef how far he has come.
Buck stayed loyal and protective if the people who carried about him and that were still alive even tho people that were called Yeehats attack trying to find Buck.