So you have the mother company: Nintendo.
It produces a game. Lets say Super Mario Brother 2.
According to how Super Mario Brother (their previous installement) sold, they produce 6 million copies (about 1 million more copies than the initial launch number and what not. Its adjusted, trust me.)
Then, they look at where their games sold.
Out of their 5 million, their Japan division moved 2 million. Their American division moved 2 milion. Their European division moved 1 million.
So at their initial shipment, they send NoJ 2.4 million copies. They send NoA 2.4 million copies and they send NoE 1.2 million copies. However, they will only release in Europe a month later because a big title was juste released in Europe.
During that time, 50 000 copies are imported from NoA to Europe. Which means that by the time the initial shipment is sold, NoA will have sold out faster and NoE will not have sold their whole quantity.