John Gills Exposition of the Bible Commentary - Isaiah 18:2
That sendeth ambassadors by the sea ,.... The Red Sea, which washed the coasts of Egypt and Ethiopia, and which were united into one kingdom under Sabacus, or So the Ethiopian, called king of Egypt, 2 Kings 17:4 and this kingdom, or rather the king of it, is here described as sending ambassadors by sea to foreign courts, to make leagues and alliances, and thereby strengthen himself against attempts made on him; though some understand it of one part of Ethiopia, on one side of the Red Sea,... read more
Matthew Henry's Complete Commentary - Isaiah 18:1-7
Interpreters are very much at a loss where to find this land that lies beyond the rivers of Cush. Some take it to be Egypt, a maritime country, and full of rivers, and which courted Israel to depend upon them, but proved broken reeds; but against this it is strongly objected that the next chapter is distinguished from this by the title of the burden of Egypt. Others take it to be Ethiopia, and read it, which lies near, or about, the rivers of Ethiopia, not that in Africa, which lay south of... read more