The military mostly recruits from the middle class now. Unfortunately, poor people often can't meet the eligibility requirements due to medical problems (especially obesity), poor fitness, criminal record, history of drug use, lack of a high school diploma, or low test scores. Of course there are exceptions but relatively few. The modern military is pretty selective in whom they take.

Many years ago my uncle got in minor trouble with the law as a young man. The judge gave him a choice: join the Navy or go to jail. The Navy worked out pretty well for him, but today he probably wouldn't even have that option to get his life back on track.