Until the 1970s, fencing was a sport restricted to the military.

the 是定冠词，用于特指某个或某些特定的事物或人。 military 是名词，意思是"军队、军方"，指国家的武装力量或军事组织。 the military 特指某个国家或地区的军队组织，在这里指"军方"。