There are three words which describe the best ways in which a country, any country, can prepare for the integration of different racial and ethnic groups into its population. These three words are education, tolerance and acceptance.
Racism, sexism, ageism, homophobia etc are not something a child is born with. They are instilled within their mind by adults who, at least by now, should know better. There is no superior race, all of humanity is related and equal; this fact should be taught to all children, wherever they happen to be and right from the moment they are born. Different ways of life, cultures and belief systems should also be taught and brought to be regarded as equal. Governments around the world should create laws to this effect.
Tolerance is all about allowing others to to be who and what they are, regardless of race, religion, sexual orientation or otherwise. Who has the right to decide what color of skin, hair, eyes or belief is right or wrong, normal or abnormal? The answer to this is clear - no-one. It should be possible for all to live side by side without fear of persecution. By educating each new generation in the right way, tolerance will become a way of life.
Every person, man, woman or child, should be accepted for who they are, rather than for what they may look like, where they may come from or what weird and wonderful god or gods they believe in. Anyone having difficulties in accepting his fellow citizens in this way needs to be re-educated.