Here's something I whipped up. Basically I expanded on my Polwank from the last thread and came up with some details about one of the wars that occurs in it. I'm not sure if it's plausible, or even good,
but here it is:
The War of the Turkish Succession
In 1867, the Sultan of the Ottoman Empire died without an heir, setting off a succession crisis. Within the Turkish Empire, sides were taken. Sakir Terzi and Nermin Aslan ended up being the two nobles who could come to rule the Empire. Aslan had fought in the Caucasus and the Sahara, and he promised to make Turkey more powerful than ever. His vision of what that meant was vague, but his promises ranged from the realistic - an invasion of Circassia and Crimea - to those that nobody took seriously, such as conquering Rome or Morocco. Terzi on the other hand, was a diplomat. He wanted to strengthen the Empire's bonds with its neighbors, especially the Arabic tribes which he claimed would eventually be brought into the Empire.
Poland and Turkey had had a surprisingly cordial relationship for the past couple of centuries (aside from the occasional war over Moldavia). The Ottoman Empire had even supported the Polish-Lithuanian Federation with its new democratic government, while most of the West was convinced that the Polish Revolution would lead to another Horatio Nelson. With this in mind, it was only natural that Poland-Lithuania would take a side in the Turkish Crisis. Terzi made sure that side would be his - promising an independent Transylvania and Lower Hungary in exchange for the Federation's support. The Holy Roman Empire set aside their historic rivalry with Poland-Lithuania to also support Terzi, for two reasons: an independent Lower Hungary would mean there was more between Vienna and the Turks than the thin strip of land that was Upper Hungary, and annexing Lower Hungary to the Empire would give the Catholic, monarchist south an advantage against the Protestant, republican north.
Persia was busy extending its reach eastwards - Russia was creeping south through Central Asia, while France's Domaine de Delhi had already made one state in the Indus Valley a vassal, it wouldn't be long before one or both of them was able to threaten Persia's borders. A destabilized Turkey would have been an opportunity if Persia wanted to expand west, but instead if the Turkish Empire fell to pieces, the Europeans might threaten Persia from the west as well, so it was in the Persian Empire's interests to end the Turkish crisis as soon as possible. Aslan was out of the question - while he'd said nothing about Persia, an expansionist Turkey was a Turkey that might decide its border with Persia could be pushed to the east.
Russia and Sweden both wanted to take a bite out of Poland-Lithuania: Sweden wanted the Federation's Baltic coast, and Russia wanted Rusynia, Galicia, and Moldavia to start with. While they'd both avoided war with Poland since the Fifth Northern War and the Horatian Wars shortly after, those had been decades ago. Now they believed Poland would be weaker - it was less than twenty years after the Polish Revolution, after all, and the Federation had not gone to war since then. So when Poland-Lithuania intervened in the Turkish crisis in support of Terzi, Russia and Sweden immediately counter-intervened in support of Aslan.
Russia, Sweden, and Poland had been the three most influential powers on the Baltic for centuries, but Denmark had a foothold in that sea too, however small, and the Danes did not want to see Sweden become any more powerful, so when Russia and Sweden invaded the Polish-Lithuanian Federation, Denmark declared war on Russia and Sweden. Seeing an opportunity, France declared war on the Holy Roman Empire with the aim of 'securing France's natural borders.' In response, the British Republic declared war on France. The war eventually spilled over into North America as well, when the intermittent wars between the colonies (and between those colonies and the former colonies that had won their independence decades earlier) resumed.
The war lasted for nine years, and would have repercussions for long after that, but in 1876 the Treaty of Budapest officially ended the fighting.
The Terzi dynasty would rule the Turkish Empire for another fifty-three years, but no longer. The independence of Transylvania and Lower Hungary would backfire as Wallachia, Serbia, Croatia, Albania, Montenegro, Greece, and eventually Rumelia started to demand their own independence. At the same time, the military had largely supported Aslan and had suffered heavy losses during the war. The remaining troops resented the Terzi dynasty, and there would be many attempted coups over the years.
France's empire had been shattered. Corsica and Sardinia were now part of Savoy, and therefore the Holy Roman Empire. The Low Countries were divided between Britain and a restored Dutch Republic. The Domaine of Delhi was the Protectorate of Delhi once more, Gujarat was self-governing again, Spain was no longer a French Domain and was in Portugal's sphere of influence, and Catalonia had been severed from France. Portugal and Britain had divided France's remaining colonies between themselves, with the exception of the Domain of Acadia which was instead forced to recognize Canada's independence and Denmark's claims in the Far North.
The Holy Roman Empire, while on the victorious side, had not come out of the war well. The Swedish and French invasions had mostly harmed the northern states, which had opposed the war in the first place. Meanwhile, the south's dreams of bringing Lower Hungary into the fold would not come to pass: first of all, Lower Hungary was not Upper Hungary - the main religion was Orthodox Christianity with significant Muslim and Jewish minorities, unlike the almost universally Catholic Upper Hungary and where Upper Hungarians mostly spoke Latin and German (except for the peasants), Lower Hungarians spoke, well, Hungarian, as well as Turkish; secondly, fighting on the same side in this one war had not erased the rivalry between Vienna and Krakow, and as the Polish-Lithuanian Federation extended its influence into the Carpathians, conflict with the Holy Roman Empire over Lower Hungary would be inevitable. With the North German Uprising of 1890-1893 and the Hungarian War of 1913-1916, the Holy Roman Empire was on the way out.
Sweden had been humiliated more than anything. With a destroyed navy, Scania lost to the Danes, Pomerania to the Germans, and Estonia to the Poles, the Swedish Empire had taken a blow. Sweden would attempt revenge in the Hungarian War, allying with the Holy Roman Empire against Poland-Lithuania, but the Central Alliance would win that war and all Sweden would get is an independent Finland.
Of all the losers, Russia had lost the least. Poland-Lithuania had taken Livonia and forced the Russian Empire to demilitarize Ingria, Ukraine, and the Russian side of the Rusyn border, but nothing more. After Russian troops had been expelled from Poland, the war in that theater had become a war of attrition, and the Polish-Lithuanian government had no interest in expanding east or losing troops by marching further into Russia than necessary.
Speaking of Poland, the Polish-Lithuanian Federation was arguably the biggest victor of the war: Livonia and Estonia were Federation territories and would soon become Republics; the Federation had proved that the Commonwealth's military strength had not diminished after the Revolution; the Federal navy had defeated Sweden
in battle, showing that the Baltic coast was finally safe; and they had the newly independent Transylvania and Lower Hungary as fellow republics and potential allies; Bessarabia would be annexed and become part of Moldavia in 17 years; and while industrialization had started decades earlier, now Poland-Lithuania would have decades of peace to complete the process.
The Kingdom of Denmark had two things to show for their part in the war: they could proceed with their aspirations in North America without having to worry about Acadian aggression, and with Scania back in Danish hands they had a slightly larger foothold in the Baltic. The Kingdom of Portugal had expelled France from Iberia and gained some degree of control over Spain and Catalonia - and on top of that, the Domain of the Bengal was Portuguese now. The Dutch Republic, while smaller in size, was free once more and controlled Delhi again, and the government-in-exile was able to return from Dutch Indonesia.
As for the British Republic, the last major war they'd fought in had been a humiliation. The War of the Turkish Succession was Britain's comeback from the Horatian Wars. They'd also gained several of France's colonies in Africa and some land in the Low Countries. Not only that, Britain could now properly consolidate its power in the Malaysian Archipelago without having to worry about French aggression. Nationalism was already on the rise, the Dravidan independence movement was about to get started, and socialists were meeting in London, York, and Manchester, but for now the British Republic was doing well.
[Yeah, when I have ideas they spawn other ideas and then the above happens. Also, I got Terzi's and Aslan's names from an online name generator that I set to Turkish. I don't know if they're realistic for mid-19th Century Ottoman nobles.]