Genetically, short hair is dominant in cats, meaning that the default setting for the hair of domestic cats is short, just as it was for their wild ancestors. But there is a recessive gene that results in long hair, and the breeding of longhaired cats was a fairly simple matter of getting together males and females who shared the recessive gene.
Where exactly this first occurred isn’t known for certain, though it was probably in central Asia (which would include Persia, the country we now call Iran). We have it on good authority that some of these longhairs reached France and Italy sometime in the 1500s, and from there they reached other countries in Europe.
No one tried very hard to be “scientific” about naming cats, so longhaired cats might be called Russian, French, even Chinese. (Obviously “Persian” was one name that caught people’s fancy and stuck.) Europeans, especially aristocrats who could afford to buy exotic beasts, were enchanted by longhaired cats, as are millions of people today.
In the descriptions of the longhaired breeds that follow, note that many of them began as longhaired mutations of an existing shorthair breed; for example, the Balinese are descended from longhaired kittens that showed up in litters of normally shorthaired Siamese.