How religion can be both a unifying and a dividing force? Use examples to explain this seeming contradiction

Religion is unifying because they allow a group of people to believe in the same thing. Black, white, brown, yellow, it doesn't matter because they could all believe in the same thing. It is also probably the most divisive subject on earth due to everyone thinking that they are right and others are wrong which is where the Christians, Jews, and Muslims usually end up conflicting with each other even though all three religions are similar.