The Polish-Swedish War (1626-1629) was a conflict between the Kingdom of Poland and the Kingdom of Sweden, primarily over control of the Baltic Sea region. The war began when Sweden sought to expand its influence in the area, leading to battles for territory, particularly in Prussia and Livonia. The war concluded with the Treaty of Altmark in 1629, which granted Sweden significant territories and trade rights, solidifying its power in the Baltic. This conflict was part of the larger struggle for dominance in Northern Europe during the Thirty Years' War era, impacting both nations' future military and political strategies.