Turkey, which is very close to Greece, used to BE a large part of the Byzantine Empire; but refer to what I said about Islam having been spread from its very start by armed conquest. The Islamic invasion which destroyed the Byzantine Empire, left Muslims in charge of a good hunk of Europe for a long time: Greece, Macedonia, Slovenia, Albania, Serbia and Bulgaria.
Mongolia is indeed in Asia, far from Europe; it borders the north edge of China. But history has been greatly affected by the physical fact that it is possible to travel nearly the entire east-west length of Asia on horses. The true Mongols (and yeah, they are Asian), together with related people known as Tatars (not Tarrrrr-tars, just TAH-tars), expanded south into China and India, then west against Russia and its neighbors. Some of the real estate they invaded and conquered had previously been invaded and conquered by Muslims; that's where the part about Mongols voluntarily joining Islam comes in.
Oddly enough, after the Tatar-Mongol Empire broke apart (and much of it was counter-conquered by the formerly-subjugated Russians), some tribes of Mongols migrated south, all the way down across China, to settle in the tropical region which now includes Thailand and Vietnam. These transplanted Mongols came to be known as the Lao Hmong (the H is silent). Where the old horse-nomad Mongols had been fierce and cruel, the Lao Hmong of recent history are peaceful and friendly.
This proves that the collective behavior of a community IS NOT determined by the RACE of its members. The group's behavior is determined by various practical circumstances, plus the FREE-WILL CHOICES of people in the community.
Mister Lewis was affirming this fact when he made the pagan maiden Aravis become a true worshipper of Aslan.