The Talmud now raises a difficulty on the assertion that there were only three kings who ruled over the whole world. First it provides a mnemonic to remember the four kings about whom it will ask (Shlomo, Sanheriv, Darius and Koresh).
The first is Solomon—didn’t he rule over the entire world? The first answer is that he was removed from his kingship. This is related to a midrash found on Gittin 68b. However, there are other opinions there in Gittin that state that after he was removed from his kingship, he was later restored. So how come he is not counted among those kings who ruled the entire world?
The answer is that Solomon’s kingship was unique—he ruled even over parts of heaven, which Rashi interprets to mean the demons. The other kings ruled only over human beings.
The next king who seemed to have ruled over the entire world was Sanheriv, the Assyrian king.
The answer is that Sanheriv failed to conquer Jerusalem.
Darius, the Persian king also seemed to have ruled over the entire world. However, he ruled over “only” 120 kingdoms. The whole world included 127, as we learn in the beginning of Esther.
From the book of Ezra it seems that Cyrus ruled over the whole earth. But the rabbis read that verse as merely a boast.