What other barriers may stand between cultures

Language because it would be hard for people to communicate. Also religion

Your friends have all listed good answers but I would like to add that land forms would also be a barrier to culture. Traditionally, cultures that are separated by water and land forms such as mountains and deserts. A good example of this would be in Papua New Guinea where they are still locating new tribes and languages. To date there are a few more that 800 on just one half on the island