In the Roman Empire, external warfare during the early centuries was notably characterized by a significant degree of peace established following decades of internal conflict. After Augustus, the first emperor, the empire flourished, and military expansion was deemed unnecessary as the existing territories were vast and stable. The most prominent military expedition, during this period, occurred under Emperor Trajan, whose campaigns attempted to extend Roman influence across the Euphrates but later faced abandonment by successors. The third century marked a turning point as internal strife rose, and the empire faced mounting external pressures from emerging Germanic tribes and the Sasanian dynasty from Iran, leading to military conflicts on multiple fronts. This section underscores how these factors contributed to the eventual fragmentation of the empire's power and stability.