The long Polish-Swedish War of 1600-1629 developed from the Swedish Civil War of 1597-98. An alliance had developed between the Commonwealth of Poland-Lithuania and Sweden towards the end of the Livonian War, and in 1587 Sigismund Vasa, the heir to the Swedish throne, had been elected king of Poland-Lithuania in an attempt to secure that alliance. Instead, it had cost Sigismund the throne of Sweden. He inherited the title in 1592, but was unpopular in Sweden, and in the civil war of 1597-98 was deposed by his uncle, Charles duke of Södermanland (who would later claim the Swedish throne as Charles IX). Sigismund returned to Poland in 1598, but remained determined to regain the throne of Sweden.
The war can be split into four phases, each split by a truce. The first phase lasted from 1600-1611 and saw Charles IX invade Livonia but suffer a series of defeats at Polish hands. The remaining three phases all saw Gustav Adolf of Sweden invade the Commonwealth, attacking Livonia during the second phase (1617) and third phase (1621-2). The fourth and final phase saw Gustav Adolf attack in Livonia in 1625 then invade Royal Prussia in 1626, before eventually making peace in 1629 so that he could get involved in the Thirty Years War.
The first phase of the war set a pattern that lasted until 1626. In 1600 Charles launched his invasion of Livonia, and an unprepared Poland-Lithuania was unable to prevent him from capturing most of Estonia and Livonia, although Charles was unable to take Riga. In 1601 the Polish-Lithuanian fight back began. In the first half of 1601 Charles suffered defeats at Wenden and at Kokenhausen (23 June 1601). In the aftermath of these defeats he convinced John of Nassau, the brother of Maurice, to come to Sweden to reorganise the army. John spent a year in Sweden without producing any great improvement in the Swedish army, which suffered another defeat outside Reval (June 1602).
Charles was crowned king of Sweden in 1604, and then led an army 14,000 strong into Livonia, where he besieged Riga. On 27 September 1605 he suffered one of the heaviest defeats of the northern wars at the battle of Kircholm, losing nearly 9,000 men in a battle with a much smaller Lithuanian army.
Over the next few years the fighting between Sweden and Poland-Lithuanian became involved in the Russian Time of Troubles, which saw both Charles and Sigismund attempt to seize the Russian throne and saw Russia and Sweden agree an anti-Polish alliance. In 1610 a Polish army defeated a combined Russian-Swedish army at Klushino (4 July 1610).
The first phase of the war ended in 1611 with the death of Charles IX during the Kalmar War. His heir, Gustav Adolf, arranged a truce to last until 1616 to allow him to concentrate on his war with Denmark.
The second phase of the war saw Gustav Adolf of Sweden enter the story. He had inherited the Swedish throne in 1611 during the Kalmar War. He had then been involved in a war with Muscovy (Swedish-Muscovite War, 1613-1617). As that war ended, Gustav Adolf was ready to renew the war against Poland-Lithuania. In contrast the Poles would have been perfectly happy to extend to truce.
As in 1600, the war was renewed by a Swedish invasion of Livonia. As in 1600 the Swedes met with initial successes, capturing a number of Baltic ports. The Commonwealth was able to regain some of the lost areas, but the Swedes still held Pernau when a truce was agreed, this time to last until 1620.
The third phase of the war once again featured Gustav Adolf of Sweden. In 1620-21 Poland-Lithuania was engaged in a short war against the Ottoman Empire. In 1621 the bulk of the Commonwealth’s army was engaged in the south, defending Chocim against an Ottoman siege. On 17 August 1621 Gustav Adolf landed at Pernau at the head of an army 17,850 strong, the largest Swedish force yet to invade Livonia. Even so, he was still potentially badly outnumbered by the Commonwealth, who had 45,000 men at Chocim alone.
In 1621 Gustav Adolf was able to win his most important victory before the Poles could respond properly. On 29 August the Swedes began a siege of Riga, then a prosperous city three times the size of Gustav Adolf’s own capital at Stockholm. The city was defended by a garrison of 300 and a citizen militia 3,700 strong. This was far too small a force to hold Riga against Gustav Adolf’s determined attack, and after a four week siege the city surrendered on 25 September. The next year another truce was agreed, this time to last until 1625.
When the war was renewed in 1625 Gustav Adolf quickly occupied Livonia. The next year he invaded Royal Prussia, quickly occupying an area in the centre of the area, which he retained for the rest of the war. Unlike in the first phase of the war under Charles IX, the Swedish armies now went on to win a series of victories over the armies of the Commonwealth, including at Wallhof (17 January 1626), Mewe (22 September and 29 September-1 October 1626) and Dirshau (17-18 August 1627). The Polish-Lithuanian forces were still able to claim some victories, such as the capture of Putzig in April 1626, which effectively prevented the fall of Danzig or the minor naval victory at Oliva (28 November 1627), but they were unable to dislodge Gustav Adolf from his positions.
In the aftermath of the defeats of 1626-7 the Poles changed strategy, avoiding battles. The infantry kept to its fortified camps, which Gustav Adolf was unwilling to attack, while the cavalry raided Swedish supply lines. This slowly wore down Gustav Adolf’s strength and began to make it clear that he could not win the war quickly. By 1629 Gustav Adolf was coming under pressure to end his involvement in Poland-Lithuania and intervene in the Thirty Years War.
In order to prevent this, the Emperor Ferdinand sent a military force to help Sigismund III hold of the Swedish attacks. On 27 June 1629 the combined Polish-Imperial army inflicted a significant defeat on the Swedish army at Honigfelde, but they too were now coming under external pressure to end the war. On 12 September 1629 the two sides agreed to the Truce of Altmark. Sweden retained control of most of Livonia and won significant trade concessions in Prussia. Gustav Adolf was now free to intervene in the Thirty Years War.