17. The Killer Bros
Early in their joint rule, brothers Attila and Bleda were challenged, but crushed the opposition. When their surviving enemies fled to the Roman Empire, the brothers invaded and forced the Romans to surrender the fugitives and agree to an annual tribute of 230 kilograms of gold. Attila and Bleda then turned their attention to the Persian Empire, which they invaded and plundered for years before they were beaten, at which point they returned their attention to Europe.
Crossing the Danube in 440, the brothers plundered the Balkans and destroyed two Roman armies. The Romans admitted defeat, and the brothers extorted a new treaty that paid 2000 gold kilograms up front, plus an annual tribute of 700 gold kgs. Soon thereafter, Attila consolidated power by murdering his brother and becoming sole ruler. In 447, Attila returned to the Balkans, which he ravaged until he reached the walls of Constantinople, before recoiling.