Why did roman leaders treat christians harshly

Romans believed Christianity to be a cult, and saw it as subversive and dangerous. They also  saw Jesus as a threat since they thought he was taking power away from kings and emperors  but Later on, however, Romans became much more accepting of Christianity, and later adopted it as a state religion. 

Roman leaders treated all religions different to their official religion harshly. Conquered regions were forced to worship their roman emperor as a god.

The answer would be a