Military service has been compulsory for all countries, until the 18th century. Today very few countries give a duty to the young citizens, since world is, at least for the majority of the countries, in a state of peace. The points to consider are two. The first one is that, a country which is less likely to be involved in a war, could spend the money to pay the soldiers in a different way. Secondly, it is not good to enforce the citizens to do military service, since they would be demotivated and it wouldn’t change their life, especially for the sedentary form of duty most of the enrolled must do.
Compulsory military service, takes a lot of time, even if it’s for only 6 months.This time can be dedicated to studies, for who, after mandatory school would like to attend university. For example, a friend of mine who lives in Switzerland, had to do one year of military service, once finished he told me that, he was payed well, but he lost the time to study medecine, which is the longest path to take, when someone wants to become a doctor, taking at least six years.
Military service is useless if it doesn’t teach how to protect your country. In Italy for example, compulsory military service has been removed during Nineties. By the declaration of people who were enrolled in that period, this occasion was not interesting, and regarded only office work.Nothing about imminent war was taught.
To conclude, I don’t think compulsory military service must be introduced, in nations that are not likely to be involved in a conflict with another country, but if needed, it must be done equally, for both men and women, otherwise it would be a violation of the universally known principle of equality, among women and men.