Why it is easy to start a clash?
It is quite simple.
Because the difference in culture is there and basically
each does not like the other come in to their backyard.

Every one agrees and accepts the difference as long as it is not
intruding into their daily life and as long as it does not enter in to their home and country. If it happens then they fight it, either openly or in stealth mode.

Ofcourse, people do change for the better..But very slowly.