The war with Poland, which broke out shortly after, overshadowed domestic political issues. In 1655, Carlo Gustavo invaded Poland, conquered Warsaw and Krakow and soon became the master of the country. The elector Frederick William of Brandenburg received East Prussia as a fiefdom from the king of Sweden. Meanwhile the Polish people were rebelling everywhere, the Russians invaded Livonia and in 1657 Denmark finally declared war. From the Polish theater of war, Carlo Gustavo made his way in forced marches to Jütland, where his situation was very critical, as the enemies pursued him from the south. Despite the terrible cold (the straits between the Danish islands, the Belts, were frozen) the king had faith in his luck and marched with his army first to Fyen and from there to Zealand. The Danish kingdom was threatened in its existence and had to buy peace in Roskilde in 1658, with great territorial losses: Sweden received Scania, Blekinge, Bornholm and a part of Norway. But Carlo Gustavo, already in the same year, again violated the peace and tried to conquer Copenhagen to reduce Denmark to a Swedish province. However, the propitious moment had passed; an assault on Copenhagen was repulsed in 1659 and the Swedish army at Fyen had to capitulate. In this situation in 1660 Carlo Gustavo suddenly died; and since his son and successor Charles XI (1660-97) was a minor, the government was again taken over by an aristocratic college. Peace was concluded with the enemies: in 1660 in Copenhagen with Denmark, that of the territories ceded in 1658 he only regained Bornholm and the Norwegian territory. Various opinions reigned within the college of government. The victorious group, headed by MG De La Gardie, in 1672 managed to conclude an alliance with France. Consequently, in 1674 Sweden had to start the war against Brandenburg. But the Swedish defeat at Fehrbellin prompted Denmark to wage a war against Sweden. The Danish fleet defeated the Swedish one in 1676 and a Danish army landed at Schonen. It is true that the Swedes defeated the Danes in several battles, inter alia near Lund in 1676, but they were unable to drive them out of the country. In the peace of 1679 Schonen remained Swedish; but Sweden had to cede some areas in Pomerania to Brandenburg. It is true that the Swedes defeated the Danes in several battles, inter alia near Lund in 1676, but they were unable to drive them out of the country. In the peace of 1679 Schonen remained Swedish; but Sweden had to cede some areas in Pomerania to Brandenburg. It is true that the Swedes defeated the Danes in several battles, inter alia near Lund in 1676, but they were unable to drive them out of the country. In the peace of 1679 Schonen remained Swedish; but Sweden had to cede some areas in Pomerania to Brandenburg.

Since the time of Gustavo II Adolfo, internal political development had led the high nobility to economic and political dominance. Its members owned vast estates in the countryside, and the former landlords of the crown’s assets were now for the most part – as well as more than one peasant, former owner – censored to the aristocracy. The most important Swedish body, the council of state, was entirely controlled by the high nobility and the main offices of the administrative offices were in their hands. Public incomes had fallen terribly as a result of the alienation of the assets of the crown.

But the dominance of the high nobility had given rise among the petty nobility, which consisted of officers and lower officials, to direct opposition from Johan Gyllenstierna. The non-noble classes were ready, as in 1650, to intervene against the aristocracy. The king joined these forces, both to improve the shaken public finances, and to increase the power of the crown, indeed to radically reorganize Swedish society. A new reduction of the assets was decided by the parliament in 1680. Later this was extended and carried out with much ardor, even with rigor. The general result of the reduction was that almost all those assets that during the century. XVII had fallen into the hands of the nobility by donation and purchase, they returned to the crown. The funds thus earned formed the basis of the financial system, created by Charles XI: several farms were assigned to the military and officials as compensation; certain fixed incomes of the state were earmarked for certain purposes and were to always cover the same expenses in the future. The king rebuilt the army on this basis and also created a substantial fleet. At the same time the king had the faculty to issue laws of motu proprio and a certain right to decree taxes; he was recognized by parliament as an absolute king. The council of state, transformed into a “royal council”, lost its ancient importance; the administrative offices were rearranged, so that the power of the king and his personal assistants increased at the expense of the aristocratic heads of the offices.

Charles XI’s reforms meant a major social upheaval. The aristocracy was ruined and lost its political influence. A strictly organized bureaucracy was created, ruled by the king; politically, the ruling class became the small nobility, whose members occupied the posts in the future. The weak side of the system lay in the organization of public finances, which were only suitable for times of peace and which did not take into account the financial needs of the crown. This became evident when the “Great Nordic War” broke out during the reign of Charles XII (1697-1718).