Ancient Assyria first rose to power in or around 1350 B.C and came to dominate a substantial empire through military might from 704 thru 681 B.C. There army was only one of the major factors contributing to there empire, a calculated campaign of terror against conquered territories was the other. Their use mass deportations to destroy any feeling of national unity was just one of the many aspects of a systematic policy of terror designed to hold a conquered providence under the sway of the King. They instituted governors to collect taxes, and exercise their military, judicial, and financial powers on behalf of the King. These systems, while under Assyrian use were despotic, later became the basis for more humane empires, such as Alexander the Great of Macedonia.
The Persian government structure was based on the Assyrian model, although, they had a much more human model of governorship. They divided their empire into 20 satrapies, or provinces. Each province was ruled by a governor call a Satrap, who in turn reported to a high official called a "Great King" which was installed in every province. This provided some form of checks and balances, and kept the Satraps from wandering too far astray. Also, they had special inspectors who traveled from province to province, reporting any wrongdoing to the Emperor. This system proved to be highly effective, and lasted for 150 years, until Persia was conquered by Alexander the Great.
Brummet, Palmira, et al. Civilization Past and Present: Volume One. 10th ed. .
New York: Longman, 2003.