There were quite a few differences that led to it.
One obvious one was the use of Greek and the use of Latin.
There was also the Authority of the Bishop of Rome.
Filioque is probably the large one that comes to mind though, as it was someone actively changing the creed to suit a theological interpretation without even discussing it as en ecumenical matter.
A lot of it was political, such as the Bishop of Rome crowning Charlemagne as Roman Emperor, when it is traditionally the job of Constantinople.
"The true Christian is a warrior making his way through the regiments of the invisible enemy to his heavenly homeland." - St Herman of Alaska.