Army reforms of 25 BC:
These demobilized excess troops after his successful war against Antony and Cleopatra,and established the strength of the Roman army at 30 legions plus a similar number of auxiliary troops.The terms of service and conditions also made the Roman army more attractive as a career,both for citizens serving in the legions,and non citizens serving as auxiliaries,who were granted citizenship on completion of their term of service.This helped spread Roman culture and assimilate the populations of conquered areas into the empire.It also made the army more professional and effective.
Administration of the empire:
Each province now had a separate governor,for civil administration,and a separate military commander. Both were appointed directly by Augustus.This made it difficult for one man to accumulate too much power in a province far away from Rome,and thus threaten Augustus' position as emperor.It also weakened the Senate,who had previously appointed provincial governors,who were always senators and who had also commanded any military forces in their province.Because all the appointees,both governors and military commanders,were now made by Augustus himself,he could choose able men that he trusted for these positions.
Decision to halt expansion of the empire:
Following the Teutoberger Wald disaster of 9 AD,Augustus decided to halt further imperial expansion, especially in Germany,and built defence lines instead (called Limes) to keep foreign armies and barbarians out.The long term effect of this was that the Germanic tribes were left in control of lands on the right bank of the Rhine - close enough to launch raids and invasions of the prosperous Roman province of Gaul in future centuries,when they had grown stronger and the Roman empire and military weaker.
