The United States should not force citizens to serve in the military. I think that all men over the age of 18 being required to sign up for the draft is service enough. Requiring everyone to serve would trample on individual freedom, which is the very thing that makes this country so strong in the first place.
Also, people tend to rebel when they are forced to do something that they do not believe in. Having angry people serve the country in such a matter could be a dangerous thing. People have varying religious and political beliefs that may not align with the military's mission.
Many European countries require that males of a certain age fulfill one year of military service, which is sometimes called universal military service. During this training, men engage in physical conditioning, weapons training, and military drills. The purpose of this is to train people in case of necessities that might arise. Citizens in many countries are given the option of other types of national service, so they do not have to be strictly in the military. There are some positive effects that come of this, such as the skills acquired and a sense of responsibility to one's country. Perhaps, America should consider something like what so many other countries do.
I'd have to reply in the negative to this suggestion. Forced service would only result in having larger military numbers, not a higher quality organization. The only time I would consider conscription as a viable resource would be in the case of a major war that threatens our nation's borders. Currently, the U.S. military is probably the strongest in the world with among the largest numbers of any country. It is not necessary to increase our armed forces nor is it economically feasible. I believe we learned our lesson in Vietnam when tens of thousands of young men were unwillingly forced into the service for a war in which many of them did not believe. It resulted in low morale and a watered down force in which many men were not adequately prepared or trained. The military is not for everyone, just as a desk job does not appeal to all people.
I assume that you mean a draft where everyone actually has to enter the armed forces for a short period, as opposed to the system we have now where all men have to sign up but don't actually get drafted. I do not think such a system would be good, but I do think that a mandatory term of "national service" would not be a bad thing.
Military conscription would not be a good idea. First of all, the military is not interested in this because they remember the problems that came when we tried to use conscripts to fight in Vietnam. They prefer an all-volunteer force for morale reasons. In addition, I do not think that it would be useful to spend the kind of money it would cost to support the much larger armed forces we would have if the whole age cohort had to serve. We would be spending lots of money for a force we don't need.
A system of national service would be better if we wanted everyone to have to "give back" to the country in some way. At least there we could have the "draftees" doing something that was more clearly useful to the country.