Yes, it's mandatory that Korean males have to do military service. Unless you are born in a foreign country and not korea then you don't have to do military service. I think the reason why Korea makes people do military service because if you look at it in a way, South Korea doesn't have much people and if they gave people a choice to attend military service, i'm surly positive that no males would go. So that could be a reason why its mandatory to do military service, also if there is a war in the future, those who went to do their military service would have experience so if more people is needed to battle, then they could be chosen to help along. I don't live in korea but everyone has to go to military for 2 years. Even idols have to attend no matter what.

Yes it is mandatory. All males from the ages 18-35 must enlist and serve in the military. Its just the law in Korea. You can be excused from serving if you have an health issue. I don't know too much about it i just know they have to do it. Even celebrities and Kpop idols. I know Yesung from super junior was just enlisted yesterday. Also big bang members are soon to be enlisted as well. :(