At its greatest extent, the Achaemenid Empire included the modern territories of Iran, Azerbaijan, Armenia, Georgia, Turkey, much of the Black Sea coastal regions, northeastern Greece and southern Bulgaria (Thrace), northern Greece and Macedonia (Paeonia and Ancient Macedon), Iraq, Syria, Lebanon, Jordan, Israel, Palestine, all significant ancient population centers of ancient Egypt as far west as Libya, Kuwait, northern Saudi Arabia, parts of the UAE and Oman, Pakistan, Afghanistan, and much of Central Asia, making it the first world government and the largest empire the world had yet seen.

Answer this question, if possible (if impossible, reply "unanswerable"): What was the largest empire the world had seen at the time it existed?
the Achaemenid Empire