The involvement of the famous Protestant general and King Gustavus Adolphus of Sweden in the Thirty Years' War gave rise to the saying that he was the incarnation of "the Lion of the North" (German: Der Löwe von Mitternacht).

Gustav and his father Erik supported the party of Sten Sture the Younger, regent of Sweden from 1512, and its struggle against the Danish King Christian II.

The German city, preferring an independent Sweden to a strong Kalmar Union dominated by Denmark, took advantage of the situation and put pressure on the rebels.

John further initiated peace talks with Denmark and Lübeck to end the Scandinavian Seven Years' War, but rejected the resulting Treaties of Roskilde (1568) where his envoys had accepted far-reaching Danish demands.

His foreign policy was affected by his connection to the Polish-Lithuanian Commonwealth; his son Sigismund III Vasa was made king of Poland and Grand Duke of Lithuania in 1587.

His Polish-Lithuanian connection came through his mother, daughter of Sigismund I the Old, and the Jagiellonian dynasty had ruled Kingdom of Poland and Grand Duchy of Lithuania and finally the joint Polish–Lithuanian Commonwealth since 1386.

However, as was often the case with the Polish-Lithuanian electoral monarchy, the outcome was strongly contested by the "losers" and a faction of the Commonwealth's nobility backed Maximilian III, Archduke of Austria.

The hostilities did not last long as Hetman Jan Zamoyski at the head of a Polish-Lithuanian army loyal to King Sigismund met and successfully defeated the Austrian troops at the Battle of Byczyna and took Maximilian III as prisoner of war.

Charles at first looked ready to negotiate but in fact he was playing for time, trying to confirm his power at another Riksdag (in Arboga), recruiting peasants for his army, and isolating Sigismund's followers.

The aims of the various factions changed frequently as well as the scale of the parties' goals, which ranged from minor border adjustments to imposing the Polish Kings or the Polish-backed impostors' claims to the Russian throne and even the creation of a new state by forming a union between the Commonwealth and Russia.

In the first stage, certain Commonwealth's szlachta (nobility), encouraged by some Russian boyars (aristocracy), but without the official consent of the Polish king and Lithuanian grand duke Sigismund III Vasa, attempted to exploit Russia's weakness and intervene in its civil war by supporting the impostors for the tsardom, False Dmitriy I and later False Dmitriy II, against the crowned tsars, Boris Godunov and Vasili Shuiski.

In response to this alliance, the Polish king and Lithuanian grand duke Sigismund III decided to intervene officially and to declare war upon Russia, aiming to weaken Sweden's ally and to gain territorial concessions.

Hetman of the Crown Stanisław Żółkiewski held a triumphal entry by the Kraków suburb of the Royal Palace, leading with him the prisoners: the Russian tsar Wasyl IV Szujski, his brothers: Dimitri Szujski with his wife - Grand Duchess Ekaterina Grigoryevna, daughter Grigory Malyuta Skuratov and Ivan Shuysky Mikhail Shein, and Filaret, the non-canonical Patriarch of Moscow and All Russia.

After early Commonwealth victories (Battle of Klushino), which culminated in Polish-Lithuanian forces entering Moscow in 1610, Sigismund's son, Prince Władysław IV Vasa, was briefly elected tsar.

Briefly, beginning in 1610, Władysław struck Muscovite silver and gold coins (Kopek) in the Russian mints in Moscow and Novgorod with his titulary Tsar and Grand Prince Vladislav Zigimontovych of all Russia.

The Commonwealth gained some disputed territories in the Truce of Deulino, but Władysław was never able to reign in Russia; the throne during this time was instead held by tsar Michael Romanov.

In the pacta conventa, Władysław pledged himself to fund a military school and equipment; to find a way to fund a naval fleet; to maintain current alliances; not to raise armies, give offices or military ranks to foreigners, negotiate peace treaties or declare war without the Sejm's approval; not to take a wife without the Senate's approval; to convince his brothers to take an oath to the Commonwealth; and to transfer the profits from the Royal Mint to the Royal Treasury rather than to a private treasury.

His relationship with the Habsburgs was relatively strong; although he was not above carrying some negotiations with their enemies, like France, he refused Cardinal Richelieu's 1635 proposal of an alliance and a full-out war against them, despite potential lure of territorial gains in Silesia.

He realized that such a move would cause much unrest in a heavily Catholic Commonwealth, that he likely lacked the authority and power to push such a change of policy through the Sejm, and that the resulting conflict would be very difficult.

His first plan was an attempt to secure a hereditary province within the country, which would not be threatened by the possible power shift following a future royal election; this, however, did not gain sufficient support in the Sejm.

Unfriendly, secretive, dividing his time between lavish partying and religious contemplation, and disliking politics, he did not have a strong power base nor influence at the Polish court, instead supporting unfavorable Habsburg policies.

Although the reign of John Casimir is remembered to be one of the most disastrous and perhaps most unsuccessful in the history of Poland and the Polish–Lithuanian Commonwealth, he is often referred to as the "warrior king" that fought bravely to save his nation and his people.

On 16 September 1668, grief-stricken after the death of his wife in the previous year, John II Casimir abdicated the throne of the Polish–Lithuanian Commonwealth, and returned to France, where he joined the Jesuits and became abbot of Abbey of Saint-Germain-des-Prés in Paris.

Before his death John Casimir intended to return to Poland, however shortly before the journey in Autumn 1672 he fell dangerously ill to the news of the fall of Kamieniec Podolski, which was seized by the Ottomans.

Nevertheless, distressed and seriously ill John II Casimir died shortly after the unexpected Turkish invasion of Commonwealth on December 16, 1672, from apoplexy and was buried inside the Wawel Cathedral in Kraków.

Upon his father's death in October 1611, a sixteen-year-old Gustavus inherited the throne (declared of age and able to reign himself at seventeen as of 16 December), as well as an ongoing succession of occasionally belligerent dynastic disputes with his Polish-Lithuanian cousin.

Gustavus intervened on the anti-Imperial side, which at the time was losing to the Holy Roman Empire and its Catholic allies; the Swedish forces would quickly reverse that situation.

His involvement in the Thirty Years' War gave rise to the saying that he was the incarnation of "the Lion of the North", or as it is put in German "der Löwe von Mitternacht".

Gustavus Adolphus was the main figure responsible for the success of Swedish arms during the Thirty Years' War and led his nation to great prestige.

After Gustav Eriksson had become king, the coat of arms was changed in the 1540s to a black vase on a golden shield, which in the 16th century was understood as a sheaf of grain or a fascine.