The German Empire (German: Deutsches Kaiserreich) is a sovereign state located in central Europe. Its mainland is bordered to the south with Austria-Hungary and Switzerland; to the east with the Russian Empire; to the north with Denmark, the North Sea and the Baltic Sea; and to the west with Netherlands, Belgium, Luxembourg and France.
Before the Empire
During the nineteenth century, German nationalism had been on the rise, especially due to the devastation that had hit the region too many times. The Holy Roman Empire had served to give them a small sense of unity, but Napoleon's victory over them demonstrated that it was not enough. However, the rulers of the small German states were not particularly accepting of the idea of losing their control over their lands.
However, it was then that a new power appeared: the Kingdom of Prussia. Slowly, the Kingdom of Prussia expanded through Germany until it held a good piece of German territory. However, its time of glory, its Golden Age, did not happen until a new Chancellor appeared: Otto von Bismarck.
Bismarck, knowing that the union of German states would not happen unless all of them found themselves with a common enemy, which there was not yet one. Thus, he started to use his political abilities and shrewdness to ensure that all of Germany was united, preferably under the control of Prussia and its King.
Starting by forming alliances with other, minor German states, and even a short-term alliance with Austria, Bismarck set out to start working on developing his nation. Two wars with Denmark first and then Austria, allowed him to form the North German Federation around Prussia, establishing itself as the most important German nation around. However, they were still away from being considered a Great Power and from adding the remaining German states (all of them in the south, near Austria) to the German nation. The only way to do that was to provoke a war with France, but one in which it was France who attacked Prussia, so as to manage to get the southern German states into Prussia's side and finally spark in their people the will to join with Prussia and become an Empire.
The Spanish Succession Crisis
The chance came when Spain exiled its queen, Isabel II, and started to search for a new king or queen to lead the nation. The possibility of placing a Prussian prince in the throne did not happen to occur to him until Eusebio Salazar y Mazarredo informed him in 1869 of the suggestion to place Leopold zu Hohenzollern-Sigmaringen as the King of Spain, and asked him for his support in that task. Bismarck soon took great excitement about the idea, since it meant potentially gaining a great ally and even possibly sparking the desired war with France.
It was then that he started to plan for that eventuality: one of his best strokes was both gaining a secret defensive alliance with the southern German states, which would pull them into the war with France if the latter declared war; another great stroke was convincing Leopold to present his candidacy to become the King of Spain, which he did in July 1870. This would spark immediate French protests, and soon after that France declared war on both Prussia and Spain.
The war soon proceeded along what Bismarck expected: the alliance with the southern German states kept the Austro-Hungarian Empire at bay, Spain's position in the south distracted France, and the French armies were soon led into a trap. The French invasion of Prussia lasted little more than a week, as the carefully deployed German soldiers managed to expel the French army from Saarbrucken some time after the city was taken. After a series of catastrophic defeats, the French army tried to oppose German counter-invasion by bringing troops from the Spanish front, but this only helped the Spanish Army to expel all French troops from Spanish territory, and to initiate a counter invasion of southern France. The Battle of Sedan seemed to be about to stop the war (as Emperor Napoleon III died there), but Dowager Empress Eugénie of Montijo chose to continue the war, hoping to be able to gain the upper hand in the negotiations. In the end, it was all for naught, and France surrendered. When the armistice was signed in the Palace of Versailles, Bismarck took the chance of such a great moment to crown King Wilhelm II of Prussia as Kaiser Wilhelm II of the German Empire.
The German Empire
After the victory against France, Germany entered in a joyous period of time. The German Empire was now a clear great power in the world, its superiority over France having been demonstrated; most German states (save for Austria) were now part of Germany; and they had a great ally and friend in Hohenzollern Spain, a friendship that was going to be important in the future.
Indeed, it would be Spain that helped Germany achieve several things they would have probably not come up with soon: for example, in the years following the Spanish defeat of the Cuban rebels, the German government authorized the development of a force similar to that of the Tercios Especiales, becoming Der Gebirgsjäger, especially trained for fighting in forests and mountains. Further collaboration came in the foreign relations department, when both nations sent the Ottoman Empire an ultimatum to get them to accept signing an armistice with the Bulgarian rebels.
Deutsches Heer & Kaiserliche
The Deutsches Heer (German Army) has its roots in the Prussian Army that fought against France during the Hohenzollerns' War. Since its victory against the French Imperial Army, the Heer has done its best to improve its weaponry and gain better training. For example, one of the first changes done was to upgrade its weaponry to the Mauser Model 1871, which would be copied by the Spanish Army at a later point in time. Another change was the formation of the Gebirgsjäger, a special forces group based on the Spanish Tercios Especiales, trained to fight in mountains and forests.
Meanwhile, the Kaiserliche drew from Spain's experimented Armada to grow and become more powerful. Instructors were sent to Kiel so that German sailors could learn to sail better. Several ships were built in German and Spanish dry docks, equipped with the most powerful motors that could be designed by the best German and Spanish engineers. Some engineers also helped in the first great project achieved by the Spanish Navy, the construction of the first submarine fleet.