There has never been a culture in human history that has remained the same since it's manifestation. Nothing ever stays the same in the universe, all cultures have borrowed ideas from other cultures and used those ideas to develop their own. Some cultures will merge with others creating a new identity while others will completely disappear because a vast majority of that ethnic group is living under the rule of a more prominent ethnic group.
These changes are happening everywhere. The faces and identities of a nation, kingdom, empire etc has never stayed the same since the beginning. Humans have been constantly moving around sharing ideas, living with one another and in some cases forcing their identity onto others through warfare.
In the present day, it is happening at a much faster rate simply because of improvements in communications and traveling technologies. So why is it that some people get upset when they hear about their child marrying outside their "race" or culture, or when they hear about immigrants moving into their neighborhoods? Things like this have been happening since the beginning of human history. "Pure cultures" don't exist and have never existed! If culture all remained pure, we would all still be living out in the wilderness hunting for our food and speaking in grunts and screeches. Hence why it is important that all cultures merge and share ideas with one another, because it allows for a culture to evolve and adapt to any of the current problems they may or may be facing that other cultures have gone through in their past due to experience.