Answer:
Religion.
Step-by-step explanation:
England was a very religion based country, as it had many historical back and forths from going from a strictly Catholic country, to Protestant. Many people were forced to conform according to whatever the religion was during that time period, and to some people that was not acceptable. A lot of people that were heartfelt Catholics felt it was betraying their religion and condemning their souls by proclaiming not to follow Catholicism anymore. It did not help that the main reason Protesism came into play was all started because King Henry the 8th wanted to marry Anne Boleyn while he was still married to his very Catholic wife, Queen Catharine of Aragon.
When Englanders came to America, it was to escape religious persecutions and to be able to follow whatever religion they chose, without fear of a ruler burning them at the stake for doing so. Hence, religion was a huge part of why U.S. seperated from England.