《资治通鉴·汉纪·汉纪二十一》
直到孝武皇帝出军北征，把这一地区夺到手，而将匈奴赶到大漠以北。在这一地区，建立城堡，修筑道路，兴建外城，派遣军队前往屯戍守卫。然后，边境才比从前稍稍安宁。
至孝武世，出师征伐，斥夺此地，攘之于幕北，建塞徼，起亭隧，筑外城，设屯戍以守之，然后边境得用少安。
It was not until Emperor Xiaowu led troops on a northern expedition that this area was seized, and the Huns were driven to the north of the desert. Castles were built, roads were constructed, and castles on the border areas were built, and troops were dispatched to garrison and defend them. Only then did the border become slightly more peaceful than before.
<s>[INST] 请提供这段文言文的现代汉语解释: 至孝武世，出师征伐，斥夺此地，攘之于幕北，建塞徼，起亭隧，筑外城，设屯戍以守之，然后边境得用少安。 [/INST] 直到孝武皇帝出军北征，把这一地区夺到手，而将匈奴赶到大漠以北。在这一地区，建立城堡，修筑道路，兴建外城，派遣军队前往屯戍守卫。然后，边境才比从前稍稍安宁。</s>
请提供这段文言文的现代汉语解释: 至孝武世，出师征伐，斥夺此地，攘之于幕北，建塞徼，起亭隧，筑外城，设屯戍以守之，然后边境得用少安。
user
直到孝武皇帝出军北征，把这一地区夺到手，而将匈奴赶到大漠以北。在这一地区，建立城堡，修筑道路，兴建外城，派遣军队前往屯戍守卫。然后，边境才比从前稍稍安宁。
assistant