In the world of Isaac's Empire, we have a Great War, and a Hundred Days War, both of which are fairly major, global affairs.
The Great War breaks out in September, 1718- and its immediate cause is the assassination of the Holy German Emperor by a Norwegian nationalist (in the world of IE, medieval Germany centralised and conquered Scandinavia, due to religious differences). The war takes place mostly along a Uniate Christian vs. a Catholic Christian split, with Uniate Portugal and Vinland initially facing off against Catholic Britain and the Reich. Other powers are quickly pulled in.
The war initially begins with an attack on Vinland by German colonial militias from New Germany and Barbarenland, which is an area that stretches from OTL New England to Ohio. Portugal declares war on Germany to protect Vinland, Britain supports Germany, and, to complete the opening phase, Spain (a radically republican and heretical country) opportunistically attacks Portugal. Portugal, a naval superpower with a relatively weak land army, is caught by surprise and quickly loses a lot of territory.
The Germans, meanwhile, fearing an intervention in the war by the powerful Roman Empire, launch a pre-emptive attack on Hungary, so that they can install a friendly Government in Budapest, and establish garrisons on the Roman frontier to dissuade Constantinople from entry into the war. Unfortunately for the Germans, Hungarian resistance proves tougher than expected, and Hungary's Polish allies choose to attack an overstretched Germany, which quickly brings the whole Eastern Front to a standstill.
The British, seeking to complete knock out Portugal, attempt to launch an attack on the coastal city of Porto Novo, which is located near to OTL New Orleans. Unfortunately for the British, their naval expedition ends in an unmitigated disaster, and the Portuguese and their allies retain total naval supremacy.
In 1719, a massive uprising in Scandinavia forces the Germans to draw troops away from the Eastern Front, ending hopes of a grand offensive to knock Poland and Hungary out of the war. In Africa, the two powerful Sultanates of Ifriqiya and Timbuktu enter the war, on the Portuguese and German sides, respectively. An attempted Ifriqiyan invasion of Spain is defeated, but Timbuktu is able to almost totally overrun the Basque colonies of North Africa. Meanwhile, the Aztecs of Mexica enter the war on the German side, and attack Portuguese colonies in the New World. Nonetheless, the war remains essentially a stalemate in its most crucial theatres.
Stalemate is broken at the very end of the year, when Russia joins the German side, and invades Poland, placing the Eastern Front in a very different situation. 1720 thus is a very different year. The small, elite state of Lombardy declares war on the so called "League of Empires", invading German Helvetia with a great degree of success. The Khanate of Persia also attacks Russia from the south, creating a pocket of breathing space for Poland. Poland is ultimately liberated by China, though, which provides the Polish with the secret of the "Dragon", IE world's first aeroplane. These innovations, plus skilled leadership, allow the Polish and Hungarians to cling to existence.
A major German defeat in Poland in the summer of 1721 prompts a coup within the Reich, which quickly becomes something of a civil war, with the Helvetians adopting the deposed Emperor, Hans II, as their true ruler. The Germans in Hamburg, decide to carry out a bloody genocide of the Helvetian rebels over the winter of 1721/22, which is responsible for the deaths of well over a million people.
The latter part 1721 generally sees the League of Empires appearing triumphant. The Germans decisively defeat the Vinlander-Iroquois alliance, and expel them from their New World colonies. Meanwhile, a Portuguese attempt to seize the British fortress-city of Williamstown on the OTL Isthmus of Panama ends in a crushing defeat at the hands of the British and Aztecs, jeopardising Portuguese control of the seas. Rhomania, meanwhile, inches closer to entering the war, under heavy provocation from her rivals in Russia and Bahrain.
Finally, in 1722, Constantinople enters the war, and the balance of power tips decisively away from the League of Empires. Poland, Hungary and Lombardy are all reinforced, and the Eastern Front begins to move westward steadily, closer and closer to German territory. The British Indian Ocean fleet is destroyed, and the British are expelled from their denuded and restive African colonies.
Desperate, now, for victory, the Germans and Spanish gamble on one last great offensive, and totally occupy the important Uniate power of Navarre-Toulouse, hoping, by doing so, to bring the war to an end with an approximate status quo. Unfortunately for them, Germany is unexpectedly backstabbed by the British at the beginning of October 1723. This reverse prompts yet another coup in Hamburg, and causes Germany's main remaining allies, Russia and the Aztecs, to sue for peace. Revolutionary Spain collapses into a civil war. Germany battles on alone for another few weeks, but finally surrenders on December 4th, 1723.
The Treaty of Prague then ensues. Which does not end well.