Adam Clarke on Revelation 2:27

He shall rule them with a rod of iron - He shall restrain vice by the strictest administration of justice; and those who finally despise the word and rebel shall be broken and destroyed, so as never more to be able to make head against the truth. This seems to refer to the heathen world; and perhaps Constantine the Great may be intended, who, when he overcame Licinius, became the instrument in God's hand of destroying idolatry over the whole Roman empire; and it was so effectually broken as to be ever after like the fragments of an earthen vessel, of no use in themselves, and incapable of being ever united to any good purpose.