There are two sets of scriptures that deal with the kings of the East. Both are in Revelation.
Rev. 9:13 and 16:2. Then the sixth angel blew his trumpet, and I heard a voice from the four horns of the golden altar before God saying to the sixth angel who had the trumpet, “Release the four angels who are bound at the great river Euphrates.” So, the four angels, who had been prepared for the hour, the day, the month, and the year, were released to kill a third of mankind. The number of mounted troops was twice ten thousand times ten thousand; I heard their number. And this is how I saw the horses in my vision and those who rode them: they wore breastplates of the colours of fire, sapphire, and sulphur, and the heads of the horses were like lions’ heads, and fire, smoke, and sulphur came out of their mouths. Through these three plagues, a third of mankind was killed by the fire, smoke, and sulphur coming out of their mouths. For the power of the horses is in their mouths and in their tails, for their tails are like serpents with heads, and by means of them they wound.

Another set of scriptures is Revelation 16:12. The sixth angel poured out his bowl on the great river Euphrates, and its water dried up to prepare the way for the kings from the east. The second verse does not tell us much. It gives us a cross-check with the Euphrates drying up, and it gives us a name for this army, “The Kings of the East”. The first set gives us more to go on. The army has 200 million men and a good description of tanks. More importantly, it gives us a set of colours that are effectively the colours of flags. Sapphire-blue, fire-red, sulphur-yellow, and white. If you look at the colours of the flags in Asia, you see them from Mongolia and Japan in the north to Indonesia in the south to Myanmar in the east. All these countries flags are made up of the four colours. From Bangladesh East, you get a complete change with greens added in. The New Zealand and Australian flags are royal blue. A very dark blue, not sapphire, so they may not be included. They are also proxy countries run by the USA and will likely be destroyed when Babylon (the USA) is destroyed.