There are many races within a religion. There are many casts within a race. There are many jaats within a cast examle:. there are many thars within Newars. Marriage is not easily accepted among two jaats even in the same Newars. Same is true in other cast such as Gurung, Limbu etc... Even in Christianity, marriage is not easily accepted across Catholic and non Chatholics. Hence your question is vague. Can you be bit specific. Thank you.