In any event, Europeans initially assumed coffee originated in Yemen, near the southern tip of the Arabian peninsula, where Europeans first found it cultivated. But botanical evidence indicates that Coffea arabica, the finest tasting of the hundreds of species of coffee and the one that hooked the world on coffee, originated on the plateaus of central Ethiopia, several thousand feet above sea level. It still grows there wild, shaded by the trees of the rainforest.
How it got from Ethiopia across the Red Sea to Yemen is uncertain. Given the proximity of the two regions and a sporadic trading relationship that goes back to at least 800 b.c., no specific historic event needs to have been involved. But if one were to be cited, the leading candidate would appear to be the successful Ethiopian invasion of Southern Arabia in 525 a.d. The Ethiopians ruled Yemen for some fifty years, plenty of time for a minor bit of cultural information like the stimulant properties of a small red fruit to become part of Yemeni experience, and eventually, its agricultural practices.
At any rate, Coffea arabica seems to have been cultivated in Yemen from about the sixth century on. It seems likely that cultures in the Ethiopia region cultivated the tree before it was transported to Yemen, but probably more as a kind of medicinal herb than as source of the beverage we know as coffee.