In Ancient Greek democracies, only a fraction of the population were actually citizens with full rights of civic participation. While the way they decided who those people were is distasteful (only free men were citizens) the concept of having a bar for who is a citizen besides who happened to be living in the city seems underrated. Institutions need to differentiate between individuals inside and outside the institution partially so that people in the in-group can make some assumptions about commonality with other people in the institution. However, under universal suffrage, the only thing that the electorate has in common is the fact that they were all born in the same country. A shared birth nation means almost nothing in a country as large and diverse as the US in a Post-consensus world.
Coupling citizenship to national service could provide a way for people to earn their franchise through a productive, egalitarian shared experience that also addresses several other problems facing the US. While national service is normally associated with military service, US national service could be expanded to other roles, as long as those roles were perceived as just as valuable and difficult as the military roles. National service would entail a two+ year tour of duty immediately after high school that provides room, board, and training but pays very little. In addition to military service, national service could perhaps include teaching and building infrastructure.
One reason I think this might work is that radical people on the right or left rarely seem to have served in the military. Of course, this could simply be because the sort of person who would become radicalized wouldn’t join a volunteer military in the first place. However, I suspect at least part of the observation is causal - the military forces people to be in life-or-death situations with people from very different backgrounds from themselves. It’s perhaps a bit kumbayah but I do believe that forced co-dependence on people with significantly different core beliefs can lead to at the very least respect. Not necessarily love, but I don’t think everybody can or should love everyone else. Respect is the important piece.
In addition to the shared experience, bubble-breaching, and civic buy-in, national service could potentially address several huge problems in US: infrastructure, teachers, and college/training. The US has notoriously declining infrastructure. National service could provide a large, cheap workforce to address that problem. In a magically awesome world, infrastructure work would also include education about how the infrastructure actually works so future generations would appreciate and build better infrastructure in a positive feedback loop. The US has a massive teacher shortage. Teaching first graders seems about as grueling as military service so it could absolutely be part of national service (as long as there was communication to make it clear how hard it actually was.) Teaching as part of national service will be controversial at first because many people would claim that teaching is a high-skill job that takes many years of training to do well. While this may be true, most teachers are thrown into classrooms with almost zero training, so three months of training might actually raise the average teacher quality. The US has a problem where a college degree has become an essential credential for most jobs, forcing people to go into debt to get a degree that is basically worthless except for the opportunities that would be closed without it. National service could act as a free bottom rung to the ladder - enabling people to signal the same positive qualities that college does, training them to do useful things, and creating similar bonds to those created in college.
We should clearly learn as much as we can from other countries with national service while keeping in mind the glaring differences. Israel probably has the most lauded national service program in the world. Instead of “where did you go to college” Israelis will ask each other “what unit were you in?” Military service kickstarted many Israeli careers, both through skills and connections they developed in the military. For Israelis who go on to university, they tend to have a better sense of how to get the most out of it starting at age 21 than 18. Singapore also has a two year national service requirement but it seems to be missing a couple of key aspects from the Israeli model. First, it only applies to men, so it’s not a shared experience though the entire population. Second, my impression is that you can buy your way out of it, or at least that wealthy people have an easier time of it. Third, people can defer it to study abroad (and possibly for other reasons.) Fourth, Singaporean national service is culturally just not respected in the same way that Israel - perhaps because of the previous three points, but I suspect there’s an additional cultural component. Culture is intellectual dark energy. Taiwan has a six month national service requirement. I know the least about Taiwanese national service but from what I can tell six months is far too short to actually train anyone so non-professional members of the military end up doing a lot of time-wasting things, barely learn anything, and everybody has a low opinion of the service because of that. Note that in two of three examples national service isn’t considered a particularly great thing. That should warn us that perhaps national service sounds better on paper than it does in practice and at the very least, it is hard to get right. There is a real danger that “do national service like Israel” is analogous to “do social welfare like Denmark.” There are innumerable differences between the US and these countries, but it might be worth calling out a few that are probably important to keep in mind. The biggest difference between the US and these examples is … well, size. Size means that it will be especially hard to keep uniformly high quality throughout the service and that people absolutely need to do things besides just military. Another big difference is diversity - Israel and Taiwan are relatively homogenous and while Singapore is pretty diverse, there are basically three main groups.
Of course, there’s the question of how to get there from here. I don’t see this happening in the current world, or being horribly mismanaged and a raging failure if it were implemented by the current US bureaucracy.