Located in present-day Poland, Prussia was originally a wild land. In the 13th century, the German Teutonic Order, with the support of the Pope, expanded eastward, occupied this large area of land, suppressed the rebellion of the local people, and thus established a Germanic state. This Knightly state relied on strong troops to occupy the entire Baltic coastal region for a time, and it was very arrogant. But by the 14th century, they were counterattacked by the Polish-Lithuanian Kingdom, and subsequently Russian troops joined in beating the Germans. After years of war, by 1466, the defeated Teutonic Knights were forced to sign a treaty, and the western territory of Prussia was annexed by Poland, and the remaining territories remained in the status of the state, but had to submit to Poland.

(Teutonic Knights)
So Prussia, though ruled by the Germans, did not belong to the German Empire, but was a dependency of the Kingdom of Poland.
In 1525, when the German princes consolidated their position through Protestantism, the leader of the Teutonic Knights, Albrecht (1490-1568), also took the opportunity to announce the Reformation and convert to Protestantism, and the Teutonic Knights state became a secular "Prussian Principality".
Albrecht did not really change for the sake of faith, he had his own calculations: in this way, the original elected position of the head of the Knights became the hereditary throne of their Hohenzollern family.
in Albrecht
Unfortunately, the Albrecht agency was too clever. When his son succeeded to the throne, he was not only a madman, but also had no male descendants, and it seemed that the newly secularized Duchy of Prussia was about to die. At this time, the other branch of the Hohenzollern family, the Elector of Brandenburg, Johheim, thought that the fat water would not fall into the fields of outsiders, and hurried to start. He had his son Sigismon (1572-1619) marry the daughter of the Mad Grand Duke. This kind of pro-kinship, coupled with Johśm's heavy bribes to the ministers of the Kingdom of Poland, finally enabled his son Sigismon to obtain the prussian succession.
So after the death of the Mad Grand Duke, Sigismon, Elector of Brandenburg, became the head of Prussia at the same time. Brandenburg, one of the seven electors of Germany, merged with Prussia, which had a martial spirit, to form the Duchy of Brandenburg-Prussia. This was in 1618.
In addition, Sigismon acquired large tracts of land in the lower Rhine and Vesy rivers, including the Ruhr mining area today, by inheriting his heirless relatives. Thus, at the beginning of the establishment of the Duchy of Brandenburg-Prussia, it had three separate territories: the Lower Rhine region in western Germany, the Brandenburg region in the central part, and the Prussian region outside the eastern part of the empire. With a combined area of 81,000 square kilometers and a population of more than 1 million, it was a powerful country among the German princes.
However, the Hohenzollern family was not satisfied. They are constantly seeking a path to territorial expansion and independence. Frederick, who succeeded to the throne in 1640. William I (1620-1688, again Frederick. Known as the "Elector of the General Election"), he vowed to make Brandenburg-Prussia a powerful state. Beginning with him, the efforts of three successive generations of monarchs have moved in this direction.
(General Election)
At that time, there were a large number of "Junker" aristocratic landlords in Brandenburg-Prussia, most of whom were descendants of knights of the past, who were the rulers of the grass-roots level. If the general election wants to enrich the country and strengthen the army, it must have their support. So the monarch and the nobles made a deal with the people. The electors recognized the junkers' right to rule over the peasantry and gave them various political and economic privileges. Juncker supported the election of the elector to build an army and the election of taxes from the cities and villages.
The Elector abolished the old army and modeled itself on Sweden to build a new army with strong fighting power, strict discipline, and let the Junker aristocracy serve as an officer. He opened a military school to absorb Junkers' children, and specially designed a very handsome military uniform, making officers a proud class in society, thus stimulating the enthusiasm of Junkers to join the army.
For Juncker, the Elector is not a pure compromise. Some Juncker disobeyed the electors, who unceremoniously arrested, executed, and even directly used the army to suppress them. He also appointed a number of able civilian officials and established a bureaucracy, thus gradually transferring state power to the monarch.
The electorate was remarkable for his "reform and opening up" and the development of industry and commerce, including overseas trade (and slave trade). He also opened his doors to European displaced people, especially Protestants. The Elector once said that "man is the greatest wealth". In 1685, for example, more than 20,000 French Protestants entered his territory, mostly rich or skilled. There were even many wealthy Jews who moved in (for this reason, the Elector's vision was much higher than Hitler's). As a result, the population of Brandenburg-Prussia increased dramatically, and the industrial and commercial and economic development was rapid.
As for the diplomatic and military aspects, the general election did not have the consciousness of "unifying Germany and resisting foreign humiliation". On the contrary, his idea of self-improvement was: colluding with foreign countries and "finding supplements" from other German princes. His diplomatic principles are: see the wind and make the rudder, the fox pretends to be a tiger, takes advantage of the fire to loot, and falls into the well.
Therefore, in the Thirty Years' War, comrade Elector went to curry favor with King Louis XIV of France and joined forces with the French army to fight the Army of the Kaiser (Austria). Thus, during the Peace of Westphalia, with the patronage of France, Brandenburg-Prussia took the opportunity to annex a large area of German ecclesiastical territory.
Later, in the Swedish-Polish War, the electors stabbed each other in two ways, one moment helping Sweden fight Poland, the other helping Poland fight Sweden, constantly betraying allies to fish for private interests, and getting the reputation of "chameleon".
In the Franco-Dutch War, the elector first accepted Dutch money, joined the anti-French alliance, and then took French money and surrendered without a fight. When most of the Monarchs of Europe were united against France, he again joined the Coalition. Later, in order to get a subsidy of 100,000 thalers (silver coins) per year from France, he concluded a secret pact with France against the German emperor.
In short, in the eyes of the general elector, allies are used to sell, and the key is to sell for a good price. The most notable achievement of the Electorate was the use of the Polish-Swedish War in which Prussia was separated from its Polish dependency. The Elector and his descendants no longer had to bow down to the Polish king. In addition, the Electorate left his descendants with an elite army of 30,000 men and a complete civilian system, as well as a top industrial and commercial base in Germany.
The Story of the Holy Roman Empire (13) The vast empire of Charles V
Tales of the Holy Roman Empire (15) Thunder! The cries of Martin Luther
The Story of the Holy Roman Empire (21) erupts! Thirty Years' War
Tales of the Holy Roman Empire (23) The Locust Marshal Wallenstein and his pig teammates