This goes back to the Situation with Madara and Hashirama... When Hashirama proposed the truce, Uchihas agreeded and an alliance formed... Madara however knew that the hate between the clans was too much and the peace would not last long, He did not want a peace treaty ..... The uchihas all shunned him for holding onto old habits and wanting to fuel more war, he eventually became the pariah of the uchiha clan...and was stripped of his title as clan head...
A little while before this Madara went blind, and his brother offered up his eyes so that Madara could see and fight again .. Of course to keep the clan on top... The peace treaty went against everything Madara believed in, but worst of all , it was like his brother gave up his eyes for nothing...
In rage Madara challenged Hashirama and lost..
Who would hold a grudge against the uchiha clan? Both Madara and Izuna would...
How would you feel if you lead a certain group to being known as one of the strongest clans to exist, And you sacrificed so much , and then they throw you away and give you no say in the matter
yup yup, Madara couldn't even go back to the village after his defeat by hashi... He seemed to have went into hiding in amagekure, which is where he would have found nagato