German Empire

Known also the Deutsches Reich, Deutsches Kaiserreich and Imperial Germany, the German Empire before the war was a military superpower, believed to be strongest in terms of pure military power. This was achieved by combination of both quality and quantity, almost limitless reserves, and great industrial might. It won several previous wars one-sided, including against the French Republic, it's archenemy.
It felt as a victim when it came to the way the world was divided. It was divided between many countries. Because of that, the colonies it got were few. It didn't sit well with the most populous nation of Europe, one that far surpassed all others. In terms of scientific breakthroughs. Military might. Industrial power. Demography.
The Entente proved uninterested in talking about establishing a New World Order. One that would properly reflect the balance of power in Europe. The feeling of superiority that the Germans had didn't help. War was unavoidable at this point, as all sides were looking for it. For a short victorious war that would ensure their vision of future would be realized.
Unexpectedly for the German Empire, winning the war proved to be much more difficult than they estimated...

Structure

The German Empire was a federal state. While the overwhelming majority of the country belonged to the Kingdom of Prussia, many areas of Germany belonged to four different kingdoms, six grand duchies, five duchies, seven principalities, three free cities and one imperial territory. The exact extent of power the emperor had over his subjects was never strictly defined and was developed in detail when need arose.
While there existed a parliament - called the Reichstag - the overwhelming majority of power in the country lied in the hands of the kaiser himself that was essentially an executive power in the country, via the chancellor (and the unofficial secretaries responsible for agriculture, war etc.). The Reichstag (divided between the Reichstag itself and the Bundesrat, the the representation of the rulers of the 'vassal' states) was more of an assortment of advisors.
Now, following the Ludendoff's Coup, all member-states fell into the hands of the Greater German Republic. The same happened to majority of the members of Reichstag, as its building was stormed early on during the coup - and most of those that weren't there, were in Wiemar that fell as well.
Because of that, the democratic elements of the government were practically disbanded, with the country changed into a de facto military dictatorship. Its head is kaiser himself. Beneath him is the Chancellor, Alfred von Tirpitz that oversees the civilian side of the current German Empire, and Paul von Hindenburg, the current Chief of German General Staff (in short, the commander-in-chief).

History

German Empire was created from the Kingdom of Prussia mostly by the realpolitik of chancellor Bismarck. Germany was united by wars with both Hapsburgs and the French Empire. Both enemies were defeated, and an uneasy balance of power was established.
The situation changed after Bismarck's death. He managed to keep the net of alliances that prevented Germany from being ostracized despite the mortal threat it posed to current world order. Those after him didn't. They only managed to assemble a Triple Alliance with Austro-Hungarian Empire and the Italy (that ended up betraying the alliance when the war was supposed to happen).
The war started because the German Empire felt harmed by the way the world's sphere of influence were divided. It wanted more territory in the east and colonies in Africa and Asia. The Entente wanted none of that; it felt threatened by the German growth in power. Because of that, war was inevitable.
Then again, nobody expected it to be so bad. The last Franco-Germanic war was pretty one-sided. The Empire wanted to repeat that. Attack France. Capture Paris. The Republic collapses. Then redirect its forces east, decimate the armies of Imperial Russia (late to mobilize due to being technologically backwards). Then, change the way the world looks like, as nobody capable of fighting you would be left in continental Europe.
The Schlieffen plan fell spectacularly during the first battle of the Marne in September 1914. A combination of many factors helped in that outcome. Russian mobilization was faster than expected. Uneeded reinforcements going east weakened the attack on Paris. There weren't enough soldiers in the west and too fast of marching speed (with German soldiers over the Marne being heavily exhausted).
What followed was the first period of trench warfare. The German Empire didn't continue the unrestricted submarine warfare, meaning that the Entente's maritime shipment was unharassed. The initiative was on the Entente side. Even the fall of Tsar Nicholas in Russia changed little, as the reorganized Russian army held their ground and even made some gains during the first Kerensky offensive.
It ended when Germany managed to find a way to breakthrough the trenches by using new artillery doctrines and stormtroopers, elite units armed with grenades and proficient in close quarters combat. What followed was the Kaiserslacht offensive. And the reintroduction of thaumaturgy to the world during the second battle of the Marne.
Another period of relative calmness on the front (called Sitzkrieg) lasted until 1920, when the Second Kerensky Offensive ended in disaster for the Republic.The German Empire achieved substantial gains east, and with the Russian Civil War starting fully, things were looking fine in the east.
In the west, however, United States of America joined the war, and the Hundred Days Offensive almost pushed Germany out of Paris. If not for the collapse of the Russian Republic, the war might've ended there. However, with the Russian Army busy shooting each other, a lot of reserves were freed and could be redirected west.
At this point, The Kaiser had enough of it. His normally boisterous personality was long gone. Too many deaths. Years long stalemate. How long was it going to last? The Napoleonic Wars, the greatest historical slaughterhouse that decimated Europe, was nowhere near this level. It was the time to search for a conclusion to the war.
The Entente, however, had to suffer one more major wound after the Russian Republic collapse. If Germany could capture Paris, bring France to the edge of collapse, the original war plan could be achieved. The Entente might be brought to the negotiation table and some decision could be made. A new Vienna Congress could be called, under a German lead, with its victory (however narrow) giving it an upper hand!
The Kaiser - after consultations with his equivalent in The Austro-Hungarian Empire - made a decision. A desperate one. War on the east was still waged, with Bolsheviks for some reason breaking their peace promises from before their revolution. A new source of soldiers to keep the frontline and free many divisions direly needed for a last push at Paris had to be found.
The Act of 5 November was issued a moment earlier, with both kaisers suggesting that some sort of a independent country would be created for Poland after the war. Of course, the proclamation lacked details. It was made merely to get more recruits and it failed spectacularly, especially after the oath crisis and imprisonment of Józef Piłsudski, the most pro-German of the polish leader.
Now, he was freed. And a new, improved act was passed. It was no longer merely a proclamation, though. The country itself was created from the lands of the former Russian Partition. Little more than the Napoleonic Duchy of Warsaw (it lacked Greater Poland but got more in the east), it was nevertheless a great boost of confidence. There were also promises (undefined closer and probably empty) of a post-war referendum in Greater Poland region... and about the lands east. It was supposed to be independent, but in an alliance with Central Powers - it didn't have to be a satellite country, as it bordered two empires at once. It was in their sphere of influence by default.
The Kingdom of Poland under regent Józef Piłsudski almost managed to actually end the war. Divisions it raised freed significant detachment of German soldiers from the eastern front. The Paris Offensive succeed, and the Entente was brought to the negotiation table.
However, the Kaiser wanted lasting peace. Germany bled during the war. He wanted some colonies and significant border corrections in the east. Then - at least two or three generations of stabilizing German colonial rule and incorporating new lands. His descendants would decide what next.
However, Germany bled a lot... and many saw anything less than total victory after all the sacrifices as betrayal. The Kaiser was almost eliminated during Ludendorff's coup. He managed to escape into eastern Prussia, and everything left of the German Empire fled with him. While Hindenburg managed to retake the capital, German Empire is still merely a shadow of its former self. It changed into an 'emergency' military dictatorship, with chancellor Tirpitz having almost limitless power (in civilian matters) with the military in the hands of Hindenburg).
The Kaiser wants the empire and the German nation to survive. Nothing more. And nothing less. Not at this point. However, while German Empire remains one of the strongest members of the Central Powers, its situation is far from nice.
The Entente wants nothing to do with it, and is busy trying to take the Greater German Republic down. The colonies are gone beside colonel (now general) Lettow-Vorbeck's dominion that actually has managed to expand, but it has no contact with the Kaiser's government. The Kingdom of Poland escaped from its leash after Germany almost collapsed, seizing Greater Poland, occupying Silesia (for now under dual polish-german government, to be solved post-war) and expanding eastward, creating sattelite Belarussia and Ruthenia.
Even if the Central Powers win the war, how will its eastern borders look like? What if the Polish-Lithuanian Commonwealth rises anew? What if regent Pilsudski attmepts to seize Pomerania as well? And the ties between Poland and Austro-Hungarian Empire seems to tighten. What if the Habsburgs decide to cooperate with the new central European power rather than the Kaiser?
The Future of the German Empire is uncertain. But if the Kaiser can retake his lost lands and reassert the German people's loyalty to him, the Empire may finally take its long-desired place as the first among European nations...

Demography and Population

The problem of the German Empire is that it cannot lose, no matter what. It managed to hold on to relatively small part of the demographic base of the pre-coup Empire. What's more, its army is still sizeable, getting close to the absolute limit that even sending women to factories won't change significantly.
Because of that, if it lose Brandenburgia, the Prussia and Pomerania might not be enough to supply the kaiser's forces with much needed reinforcements... and the German Empire will collapse on itself. It is a looming threat and a cause behind using White Russians and Balts to hold the frontline east. All hands are needed west now.

Military

Despite everything that happened, kaiser's army remains strong. It might have lost majority of its numbers, but it lost nothing when it comes to equipment and morale. It suffers, however, from an increasing logistical problems due to lack of control of all German major industrial regions.

Foreign Relations

War with Entente and Axis. Neutral to Holy League. Its problem is that there is a growing disagreement between the Empire and Kingdom of Poland that might threaten the stability of the Central Powers.
There is a lot of mutual dislike and distrust in polish-german relations. It might already end up in a war... if it wasn't a de facto suicide because of being surrounded from both sides by Axis members.

Gott Mit Uns

Important Characters

Government
Kaiser Wilhelm II
Third emperor of the united German Empire... currently very busy making sure he isn't also the last one of them. A symbol of unity of the still free parts of the Empire.

Alfred von Tirpitz
A creator of a German Empire fleet, elevated into the seat of Chancellor following the Ludendorff's coup to make sure that German Empire is ready to wage total war against the Entente and Axis - mostly because kaiser trusts him.

Paul von Hindenburg
Fieldmarshal of the German Empire, Chief of the German General Staff, and Empire's current de facto commander-in-chief. Monarchist, conservatist and a German nationalist, but far from the level of insanity his former co-worker, Ludendorff, shows....

Albert Einstein
A winner of Noble prizes for his achievements in physics and the theory of relativity. Made a head of the Kaiser Wilhelm Thaumaturgie Institut after he turned out to have an aptitude for thaumaturgy.