What is the difference between the Persian and Assyrian empires?
The Assyrian Empire enjoyed a much longer history than the Persian. It was one of a collection of nation-states in the ancient Near East that persisted more or less continuously from the 3rd millennium BC until its spectacular fall in 612 BC. Ancient Assyria was located in northern Mesopotamia, bordered to the south by Babylonia, to the north by Mittani and the Hittites, and to the west by Egypt. These states traded and warred with one another during much of the 3rd and 2nd Millennium BC.
With the rise of the Middle Assyrian Empire in approximately 1400 BC, however, the balance of power began to shift and Assyria began to dominate its neighbors. Assyria conquered Mittani and Babylonia during this period, and only an alliance between the Hittites and the Egyptians prevented their further spread. During the Bronze Age Collapse, Assyria survived the incursion of foreign invaders that marked this period and entered the classical period of antiquity in a strong position. During the Neo-Assyrian Period beginning approximately in 900 BC, the Empire once again spread over the entirety of Mesopotamia, but this time went further, conquering the Levant, much of Anatolia and Persian territories to the east. Incredibly, during the last century of its existence, the Assyrians even conquered Egypt and their empire reached its greatest extant.
The Assyrians were trailblazers. They developed the first professional army in history, which was heavily reliant upon the chariot. With this large, well-trained army, the Assyrians conquered the first multinational empire in history. They maintained control over their subjects through terror. Assyrian reliefs taken from palaces in Nineveh and Assur relate gruesome tales of mass executions and describe the destruction of cities like Babylon almost gleefully. These acts not only helped quell dissent but also furthered Assyria's expansion as enemies who resisted could expect brutal subjugation, as was the case of Babylonia, or outright extermination, as in the case of the Elamites and the Mittani. So many opened their gates when the Assyrians came in force.
The downside of rule through terror became apparent with the sudden fall of Assyria in 612 BC. Assyria's ruin was actually brought on by its expansion; the empire became the first victim of imperial overstretch, possessing more territory than it could actually administer. Further, expanding its borders brought Assyria into contact with new enemies such as the Medes, Cimmerians, and Persians, who were strong and practiced novel ways of fighting. A coalition these enemies was joined by a resurgent and vengeful Babylon in 612 BC, and in quick succession, the great cities of Assyria were sacked violently and the Assyrian Empire was destroyed, never to rise again as a player in the Near East.
Assyria laid the groundwork for the Persian Empire by unifying and subjugating much of the land that the Persians would later conquer. In a sense, Assyria softened up much of the region to the conquests of the Persians, Greeks, Romans, and Arabs. Cyrus the Great, the founder of the Achaemenid Dynasty, led a revolt against Medea, one of the Kingdoms that had conquered Assyria only a half century earlier. He would then, within one lifetime, conquer much of the territory it had taken Assyria centuries to acquire. His descendants would reconquer Egypt and extend Persian control into central Asia and India, creating the largest land empire in history up to that point.
As rulers, the Persians generally had a lighter touch than the Assyrians. The Persians named regional governors over their conquered territories and allowed conquered lands to maintain a certain degree of independence. The Persians were certainly capable of using terror as a ruling strategy, but it was not their preference, and they didn't revel in it the way the Assyrians did. The Persians also did more to foster commerce and cultural interaction through the building of sophisticated road networks and the development of coinage.
In contrast to Assyria, when Persia fell, it was not an internal uprising or a coalition of enemies that brought it down. Rather, Alexander the Great led one of the most remarkable military campaigns in history, essentially conquering the Persian Empire whole after a series of brilliant victories. That Alexander kept much of the Persian infrastructure and bureaucracy in place is a tribute to how well it functioned. That, rather than supplanting Persian culture with Greek, Alexander attempted to fuse the two shows that he admired much about his newly conquered subjects. We see no such admiration for the Assyrians. One of the most important sources regarding the Assyrian Empire is the Hebrew Bible, which essentially curses the Assyrians for Sennacherib's conquests of the Kingdoms of Israel. When Assyria fell in 612 BC, the Bible's condemnation states "Who shall bemoan her?" Cyrus the Great, on the other hand, is praised in the Bible for ending the Babylonian Captivity and allowing the Jews to return to Israel.