The approach to this solution we find in Rev. 17.10 ff :

"There are also seven kings. Five have fallen, one is, and the other has not yet come. And when he comes, he must continue a short time."

The Book of Revelation has been written in Roman times.   So:  The 6th head with his  followers governs Rome now.

The 7th head then begins his reign with the downfall of Rome in the year 1453.

Whom can we assign the first 5 heads?

                                    Head 1 reigns Babylon.

                                    Head 2 reigns Persia.

                                    Head 3 reigns Greece.

Daniel 7.6 says, that the leopard "Greece" has 4 heads.   This means, that Greece is governed by 4 angels.

Is there a hierarchy, then only one has the power. Of course. But here are 4 angels equally entitled.

How is this to understand?

If there is a picture and we have its black-white fraction, its red-white fraction, its yellow-white fraction, and its blue-white fraction, and we print all those fractions on top of each other, then we have a colored picture.

 So our perception. We describe this with the concept "fourfold".

Only the Greek could say: "The whole is more than the sum of its parts."

The colored picture is more than its mono-colored parts. The "fourfold" is more than the sum of its parts - than the sum of its angels.

The Greek people have been equipped with an unusual great spiritual power.   Which deity should they offer their thanks?

They have been equipped with a greater spiritual power, than any angel could give them.

This high culture of Greece ends with Alexander in the year 323 BC.

Alexander's world divides after his death into the 4 Diadochi empires. Two empires have no contact with Israel. But Great-Babylon and Egypt as the "King of the North" and the "King of the South" determine the fate of Israel. (Dan. 11)

Those two countries now are under the reign of the angels 4 and 5.