Scientists have discovered that the collapse of the Roman Empire 1,500 years ago was caused by the miscalculation of their Persian-Sassanian opponents, which led to the loss of critical trade routes. The economy quickly collapsed, forcing people to flee to other regions. Previous research had suggested that a plague decimated the empire, but the new study found that it was at the height of its power, economic output, and population. The researchers also found that climate change and the Justinianic plague were not significant factors in the decline of the empire.