(Based on VIP 4B)
Although not the most promising minor state, Serbia has incredible potential, if you’re patient and willing to be very manipulative of the larger powers around you (as well as the historical events that shaped the Balkans in the Nineteenth Century). With a little skill and a lot of luck, you can create Greater Serbia and finish in the top 20.
Serbia is surrounded by hostile states with far greater power and resources. The key is understanding that Austria is your friend. Don’t antagonize this Great Power – no matter how much you’d like to get your hands on Bosnia. The Ottoman Empire is the real enemy. Keep your focus on claiming territory from the Sick Man of Europe (as well as the smaller states to your east) and you’ll be in good shape. Furthermore, you start out as a satellite state of the Ottomans – this prevents you from pursuing an independent foreign policy, so it will be the first thing you need to address. Your country also contains a mere three provinces, allowing any enemy to annex you in one go. It’s important not to go to war until you’re sure you can acquire more territory to avoid being knocked out of the game by any predatory combatant.
You also lack an outlet to the sea, and it’s unlikely you’ll acquire one before the 1870s or 1880s. Put aside visions of overseas empire until you’ve had a chance to build up the home base, and only then start looking abroad.
Russia is well inclined towards your little kingdom and this is a friendship that you’ll need to nuture if you hope to move forward. Greece is also a friendly state. It’s not terribly important earlier in the game, but when you start moving to take advantage of the growing weakness of the Turks, you’ll want to solidify this relationship.
You also begin the game with some key resources. Your home provinces produce both coal and timber, which will give you a leg up on industrializing. There are sizable Serbian populations to your south (in Montenegro and the Turk lands) and to your north (in Austrian-controlled Hungary). Keep these in mind and look for ways to bring them into the fold if you want to survive the bloodshed of the first half of the game.
First step to greatness: Become truly independent
Begin the game by getting your economy in order so that you’re not bleeding money every month. Don’t worry too much yet about pursuing research – you’re going to need cash for the revolution that will free you from Ottoman overlordship. Once you’ve built up a nice reserve (by the early 1840s), disband your only military unit and change your voting rights to Wealth. This will briefly make you a constitutional monarchy. When the inevitable counter-revolution comes, choose the liberal outcome. This will cause revolts across your nation, but once they’re successful in restoring your despotic monarchy to power, your satellite status with the Turks will be broken and you’ll be free of their control.
Take on Hungary
As the Liberal Revolution nears, build a dragoon unit, but don’t place it just yet. Wait for Hungary to declare its independence from Austria. Once things start going badly for Austria and its allies, they’ll begin to ask you to form alliances. The best-case scenario is that Russia is fighting on Austria’s side against Hungary – if so, turn down the offers you receive until Russia invites you into an alliance. If Russia is sitting this one out, wait to join the war until things start looking grim for the Magyars. Take up an alliance partner who offers you a full treaty, place your reserved unit to the far East, then invade one of the Hungarian provinces. If you time this right, the Hungarians will invade with a fairly small army, so you’ll be able to capture one of their provinces long before they can take one of yours. Then start offering them a peace treaty – try to take as many provinces as possible. I’ve been able to come away with a full four territories (several of theirs are yours by right). The key is to capture Hungarian land before they return it all to Austria. Try to emerge from this war with an expanded territory to the north – which may also give you craftsmen and clerks to fuel your industry in a few years.
Prevent Romania from emerging
Once war with Hungary is over, you’ll want to begin the conquest of Wallachia. You need to attack before the Austrians guarantee its independence (and will need Russia’s help to make the first annexation). Generally, the best you can do in the first war is to take Pitesi (which has more coal) and then render the rest of the country your satellite. In the late 1850s go back and take the remainder of the country – the key here is to do so before Wallachia and Moldavia unite to form Romania. You don’t want this rival on your eastern flank, and you’ll also want to take the craftsmen and clerks there to fill your factories.
Be sure to end your alliance with Russia before the Crimean War breaks out. There’s no way you can take on the Ottomans right now – and you’ll be able to restore this alliance later when you need it.
Focus on industrialization
The late 1850s and the 1860s you need to push your research and acquire Mechanical Production. Once you do, build glass and lumber factories in Serbia. This may push you into debt, but it will pay off in the end. These factories will absorb the workers from your conquered Hungarian and Wallachian provinces, so you won’t need to convert POPs of your own.
Take on Turkey
Your next big event will be the Serbo-Turkish War in mid-1876. Ally yourself with Russia, Austria, and Greece – pay whatever you need to improve relations and make sure you have offensive alliances. Just before the war, you’ll be given some extra units and leadership. At this point, you can create two strong Serbian generals (make sure you create one well before you’re given the extra points). You’re not going to capture much territory in this war – although Montenegro will join your side, the Russians will force you to surrender Bosnia to the Austrians and you’ll just get two provinces. But right after this war ends, the Russians will go to war with the Turks on their own. This is when your alliances are key – when your DOW the Turks again, you need to make sure the Austrians and Greeks come with you. With luck, you’ll end with another province or two. Then the cash will start rolling in, you can begin to build railroads, and you’ll be in fine shape.
Bring Montenegro home
This little country is mostly Serbian, so take it in the 1880s to further increase your territory. Its independence is guaranteed by Russia, but if your relations are good, they won’t intervene. They'll have taken one additional province back in the Serbo-Turkish War in 1877, so there's even more to gain.
Finally, stretch your wings
Now you’re on your own. By this point, the Russians will probably control Constanta on the Black Sea, but you can buy it from them and acquire your first port. Keep the research up and start looking for weak countries abroad to take as colonies. (If Tunisia is still independent, this is a good place to start – it annoys the Ottomans and gives you the beginning of an empire.)
Look for opportunities to conquer Moldavia, plan an invasion of Greece, or annex Bulgaria is you’ve the resources to fight off the Russians on the way. If you’ve played your cards right, the Ottomans should be increasingly weak and you can set your sights on the rest of the Balkans and even make inroads into Asia Minor. Watch for a chance to take Bosnia (rightfully yours, after all) back from Austria -- but be sure she's deeply embroiled in some other conflict before waking this particular dog.