Who were the first people the Persian conquered in establishing their empire?

The first people the Persians conquered in establishing their empire were the Medes, around 550 BCE. Under the leadership of Cyrus the Great, the Persians united with the Medes and then proceeded to conquer other neighboring tribes and kingdoms, including the Lydians and the Babylonians. This marked the foundation of the Achaemenid Empire, which expanded significantly under subsequent rulers.