Example of the long term impact is: A) the spread of Eastern Orthodoxy into Russia
After Byzantine empire Conquered a certain region, they required the people in that region to follow their religious teachings. In the past, Current Russian land was part of Byzantine's influenced region.
Because of this, Eastern Orthodox teaching (which adopt the values and rules introduced by the bynzantine empire) still really popular in Russia even to this day. Approximately, around half of the total eastern orthodox lives in that country, while the rest are spread nicely among the neighboring countries.
Compared to the more modern christian groups, Eastern Orthodox is considered to be more traditionalist/conservative. They require the members to follow a stricter rules than other christian groups.