Answer:
ideas and cultures are exchanged for a number of reasons, i'll list a few.
1) some people, and cultures, love to try and shove their religion on others because they think there's is the best. so religions could be spread this way.
2) with so many things going on in the trade process, sombody eventually thinks that somthing that Another Country is doing is going to help them out in a personal or finacial way and they adopt that for their own personal use.
3) you can research some more yourself, i just took a test on this and it took me a while to find the stuff, most people don't like helping with things like this.