I don't think, that nation is the most important quality in such relationships. We live in 21-st century. If 2 persons love they will be able to understand each other and find a decision, which are available for both. We ourselves choose our path in life and decide what traditions to follow and what religion to manifest. However, I can agree, that people with same nation probably will be closer to each other. They will not have to explain each other simple things in everyday life, they will have less differences, because of that less difficulties. But despite everything inter-ethnic marriages are possible and many couples have a big chance of a successful relationship) Because the main quality of successful and happy marriage is character, respect, love and other spiritual qualities)