The correct answer to this open question is the following.
Although there are no options attached we can say the following.
Roman military policy changed under the emperors Trajan and
Hadrian in that both Roman Emperors did not pursue conquest and territorial expansion of the Roman Empire as other Emperors did.
Both Emperors focused on other political and social activities in the Empire and did not prioritize war and territorial expansion using their military force and powerful armies.
One of the most important battles in times of Emperor Trajan was the invasion of Dacia, an important territory that had mines that were exploited by the Romans.
In the case of Hadrian, the Emperor mostly used the Roman Army to defend the Roman territories from invaders.
