How was the Persian Empire formed?

Answer 1

Persia, a subsidiary state to Media, incorporated it and used this combined strength to absorb the Middle East, then expand to North Africa in the wast to today's Pakistan in the east.

With the Indus River in the east and the Mediterranean Sea in the west, it thought it had established defensible frontiers, however the Greek cities in Asia Minor were restive and led it to war across the Aegean Sea with the mainland Greek cities. This came back to bite them when Alexander the great invaded and captured the Persian Emoire.