I wouldn't think of it as ruining, personally. Sure teenagers here eat hamburgers like just any other snack by now, while I still clearly remember it as a big treat from my dad every once in a blue moon not too long ago; that doesn't change the fact that they still go to school 6 days a week, they still can't sue their parents any time they get spanked with a stick, regardless its size. I believe I won't be seeing highschool kids taking each other out for pizza for dinner as a "what's special about that" deal yet in the next 10 years.
Culture is formed after a long long time of daily lives, and life moves on, therefore every culture is subject to adaptation, given that there is change. During the time it takes for one culture to shift in its direction (regardless of external affluences), the affecting cultures would've shifted to their new forms, thus there is no real "ruining" any culture. That's, in my opinion, for old people and their stubbornness.
Speaking for my country, be it the US or Japan, France, China, all of who have once colonized us, we share part of their cultures. We're heavily influenced by Chinese culture due to the fact that we were a part of them for too long, we have no other words beside "cafe" to refer to coffee and I don't see that changing any time soon, we make curry with Indian curry powder and we use Microsoft's Windows OS (cracked by the Chinese though). Can I say our culture has been ruined by any of those countries? I think otherwise. Those cultural traits form our specific culture as it is known today.
As for two-way influences, I'm not too sure but I'm under the impression that money/power talks here. Maybe Quantact could give you a better historical insight but I'd say we look at the role models of history. Then again, China has Dim Sum and we have Pho almost everywhere by now. It probably is decided by an internal factor of each cultural trait itself. If one thing possesses enough value in one culture, it gets integrated in, otherwise, rejected.
Culture is formed after a long long time of daily lives, and life moves on, therefore every culture is subject to adaptation, given that there is change. During the time it takes for one culture to shift in its direction (regardless of external affluences), the affecting cultures would've shifted to their new forms, thus there is no real "ruining" any culture. That's, in my opinion, for old people and their stubbornness.
Speaking for my country, be it the US or Japan, France, China, all of who have once colonized us, we share part of their cultures. We're heavily influenced by Chinese culture due to the fact that we were a part of them for too long, we have no other words beside "cafe" to refer to coffee and I don't see that changing any time soon, we make curry with Indian curry powder and we use Microsoft's Windows OS (cracked by the Chinese though). Can I say our culture has been ruined by any of those countries? I think otherwise. Those cultural traits form our specific culture as it is known today.
As for two-way influences, I'm not too sure but I'm under the impression that money/power talks here. Maybe Quantact could give you a better historical insight but I'd say we look at the role models of history. Then again, China has Dim Sum and we have Pho almost everywhere by now. It probably is decided by an internal factor of each cultural trait itself. If one thing possesses enough value in one culture, it gets integrated in, otherwise, rejected.