Crthuky

I am the dictator of a nation with a population of 350 million people. In order to keep our nation strong and independent, I have decided to institute a nationwide combat preparation program in which citizens would be taught some degree of military training in order to prepare for war or defense of the homeland. All people would go through this program before entering the workforce or going on to higher degree of education. Upon completion of the program, people invested in having a career in the military would go on to enlist, continuing to train their entire lives. All others would go back to being good and productive citizens.

There are some nations such as Israel that has mandatory conscription for all citizens over the age of 18. A much larger nation called the Soviet Union tried this and proved successful for a time, bwgore collapsing due to economic and political instability. Is it feasible for me to do the same for my nation, which has a much larger population? How can I make this happen successfully without causing unintended negative consequences for the nation?

Sure, why not? The Soviet Union had mandatory military service pretty much EXACTLY like what you're describing with a population that size. The factors that would make it difficult to have nationwide combat training have everything to do with politics (your population refuses to participate) and economics (you can't afford to have all those people not producing food), and nothing at all to do with how big your country or population is.

In addition to the Israeli Defense Force, you have the Swiss Militia, which has manditory conscription, and the United States, which has one of the largest volunteer forces in the world. (China and India have larger active duty numbers, because they are both one billion strong populations. Of those three, Per capita, total active duty U.S. Military forces is 4.2 persons per 1000 citizens, where as China is 1.5 persons per 1000 citizens and India is 1.1 per 1000). The United States also has a population just slight under your nation's, and aside from the active duty and reserves, has a highly armed civilian population, with 100,500 guns per 100,000 citizens. Yamamoto famously cited this as one of the reasons Japan really really really should think twice about winning a war on the U.S (they didn't not that it got to that point... though it should be pointed out that the United States Civil War is still deadliest war in it's nations history and remains the deadliest war fought in the Americas ever) and it did practice conscription in World War II, so it can be scaled up.

While I'm not familiar with the Israeli system, the Swiss system is basically founded on the belief that citizenship also entails some obligations to the community, so all citizens by law perform community services upon reaching age 18. This is most typically seen as military duties, but many community fire departments, EMS services, and other services are staffed by people performing this duty time. Conciesnous objectors can either opt to a non-gun service or join the military in an unarmed role (usually a combat medic, which can't carry weapons per rules of warfare or chaplins, who cannot do this either). Typically this involves a 30 week duty period plus a period of time as reservist status if not choosing to be a career military (enlisted typically leave reserve status at age 30 and officers at 34). Reservist famously took their standard issue weapons home with them along with bullets for the weapon that were regularly checked to ensure they were not used without instruction, though this practice was abolished recently, and now the reservist will have to report to the near by ammunition depot for his ammo and, if choosing to not keep it in the house, his weapon. Switzerland is very mountainous and many of their defensive strategies involve forcing hostile forces into narrow passes which are basically shooting galleries. It was once joked that a Nazi General once met with a Swiss General and and asked "What would the Swiss do if I marched into Switzerland with an army a million Germans strong?" The Swiss General Responds "Well, then I would meet your army with an army of a million Swiss and we would each shoot once and then go home." The Nazi General smiles, and says, "Suppose I come with army of Two million men strong, what would you do then? (About a quarter of Switzerland's total modern population)" The Swiss General answered "Then we would shoot twice."

With any military, it's also not about shooting... but who helps you too shoot. An accepted rule of the military is that for every man on the front line, their are four men behind him in support tasks (food, supplies, logistics... a military marches on it's stomach), which is why the United States is such a formidable foe. The United States military invests a ton of money in getting supplies to the boys "Over There" as the World War 1 song calls the war front. World War Two implemented rationing when it wasn't needed so that supplies could go to front lines, and while the rest of the world was marching to the battle lines, the U.S. brought jeeps and drove... There's something to be said for troops that drove 35 miles fighting troops that marched the same distance. And while the U.S. has done conscription since the Vietnam war, signing up for the Draft is still required by all male citizens, and again, they arsenal of civilian weapons knows no equal in the world. It's long been understood that an invasion of the United States would be damn near impossible by the huge territory alone, but the fact that the population is heavily armed. As one of my friends observed The Swiss' gun culture is strongly informed by fear of the threat of outside governments invading it, but the U.S. gun culture is informed by the fact their own government was once the enemy (and now we call it the UK)... so the people who own guns in the states, more often than not will be more than willing to admit that if the day comes when the government will turn against the people, they will shoot the government... and if they are willing to do that to their own government, what do you think the attitude to invading forces would be.

Where I see problems with your hypothetical nation though is something that the U.S., Swiss, and Israeli countries have, which is a strong sense of democratic self and the idea that it's up to the people to fight for the nation. This is an attitude not often found in a dictatorship in general, which may have to control for more descent in the ranks of the conscripts than the United States, Swiss, and Israeli forces have to put up with. The Swiss is very neutral and their military exists to ensure it doesn't go to war, the less I discuss Isreal the better... But they've had a lot of wars in a very short history, most of which leave them surrounded but for the ocean, and citizens tend to be committed to defending themselves. In the United States, starting wars has been a rare recent affair, and they've only truly do int with the volunteers only... conscription tends to happen when they've been attacked and wish to defend the nations ideals. You'd most likely need to really work around how you can get your common man to understand the need for his conscription into service is good... or all you do is arm your rebellions.