What was the main issue leading to the separation of jews and christians in the post-apostolic period?

The main area of division was around circumcision and observance of mosaic laws.
As time went by, the church became increasingly gentile,separating itself from the ideals of mosaic law and issue of circumcision.According to Cohen, early Christianity ceased to be a Jewish sect when it ceased to observe Jewish practices, such as circumcision. However,historian have called on caution as the separation was not a single event but a historical process.