The presence or absence of some form of conscription is a major social policy variable, but it's often difficult to study its impact since in the places where it exists conscripts are generally teenagers. An exception to this in the recent past was Portugal, where men were generally conscripted at the age of 21. That means that many of the conscripts had pre-conscription earnings history that David Card and Ana Rute Cardoso were able to use to study the impact of military service on wages. The net result seems to have been negligible, but very low educated men appear to have benefitted:
Although military conscription was widespread during most of the past century, credible evidence on the effects of mandatory service is limited. We provide new evidence on the long-term effects of peacetime conscription, using longitudinal data for Portuguese men born in 1967. These men were inducted at a relatively late age (21), allowing us to use pre-conscription wages to control for ability differences between conscripts and non-conscripts. We find that the average impact of military service for men who were working prior to age 21 is close to zero throughout the period from 2 to 20 years after their service. These small average effects arise from a significant 4-5 percentage point impact for men with only primary education, coupled with a zero-effect for men with higher education. The positive impacts for less-educated men suggest that mandatory service can be a valuable experience for those who might otherwise spend their careers in low-level jobs.
This is not a good reason to start a nationwide conscription program but it is a useful datapoint for thinking about human capital issues.