Upvote:3
As summarized in the Wikipedia article on the Second Persian Invasion of Greece, Herodotus lists 47 diverse ethnic groups which together constituted 1.7 million infantry troops, a large share of Xerces' 2.6 million forces. Whatever the accuracy of these numbers, Xerces clearly recruited soldiers from far and wide, and there may not be anything particularly special about the presence of Ethiopian ethnicities among the others.
Upvote:13
The "Aethiopia" of Herodotus was not the same thing as modern Ethiopia. Rather, the term described anyone from non-Mediterranean Africa. At the time of the Battle of Thermopylae, the Persian Empire included part of Aethiopia, so it's not surprising that an army composed of soldiers from all over the empire would include some Aethiopeans.
Upvote:18
From the Oxford English Dictionary (1928):
Ethiop...
The Ethiopians are mentioned by Homer as a people dwelling in the far east and far west; in later Gr[eek] the name was applied chiefly to the inhabitants of Africa south of Egypt, but also to people of swarthy complexion from other parts of the world.
Under the heading for Ethiopian it further mentions that this usage is also attested in English, from the 17th century, as a generic expression for black-skinned people.
So in the quotes inquired about, the usage is likely not specifically to peoples from the area now known as Abyssinia, but rather to swarthy or black-skinned peoples.