Adam Clarke on Ezekiel 37:22

I will make them one nation - There was no distinction after the return from Babylon.

And one king shall be king to them all - Politically speaking they never had a king from that day to this; and the grand junction and government spoken of here must refer to another time - to that in which they shall be brought into the Christian Church with the fullness of the Gentiles; when Jesus, the King of kings and Lord of lords, shall rule over all.