I have a hard time explaining to my children the reason borders even exist. It is the same with the various currencies. They often say it would be so much easier to travel without having to exchange money.
I believe, deep down, that we are all brothers and sisters. We live in one world, which is planet earth. We are all the same on the inside, whatever our skin shades.
Imagine there are no countries and people could travel easily. Imagine there are no separate lines at the airport when we show our passports to the police. Imagine countries would be treated as equals and their inhabitants as only one family.