I do not believe that the kings of the east must come from east of the Euphrates, or China and/or other far eastern nations. If you look up the words alone you will find that the kings of the east have always been in the neighborhood and were Israel’s enemies from surrounding nations. Just look up the term in the book of Judges alone! The Word of God repeats itself as to theme and function and I believe that these same “kings of the east” that always troubled Israel will be a confederacy of Islamic near-by nations. They can make up the large number if you combine the players of Ps. 83 and Ez. 38. We need not go to Korea, China, etc. This doctrine started with Hal Lindsay’s Late great Planet Earth but I don’t think it follows a clear path of scripture and its repetition. As we await the coming of the Lord in the clouds for us we certainly see a growing hatred of Israel in the surrounding nations. By this alone and the veracity of scripture I don’t believe we need add into the Bible things it doesn’t really say. This is mere speculation.
If you don’t believe the Kings of the East have to come from East of the Euphrates what do you do with Rev. 16:12? “The sixth angel poured out his bowl on the great river Euphrates, and its water was dried up to prepare the way for the kings from the East.”
Daniel 11:40-43 talks about the Kings of the North and South coming out to challenge the anti-Christ. In the context of Daniel 11 these two Kings controlled all of the middle east including the countries mentioned in Psalm 83 and the middle eastern partners from Ezekiel 38. But after defeating them the anti-Christ is immediately alarmed by reports of an enemy coming from the East. Who is that?
And it seems clear that the Great Tribulation is world wide in its scope. Rev. 9:13-16 talks about one third of the population dying because of some force released by four angels stationed at the River Euphrates. 60 % of the world’s population lives East of the Euphrates. Do they just sit this out? If so then out of the remaining 40% who live in the West, all but 6 2/3% will perish. It sounds to me like you’re trying to turn the Great Tribulation into a regional conflict, at the end of which only the Asians will be left standing to receive the Lord.