The last of Vasa's sons, his heir was the seventeenyearold Gustav II, better known as Gustavus Adolfus. The rule of Vasa and his sons made Sweden a nation, culturally as well as politically. The courts were filled and influenced by men of learning; art and sculpture flourished. The Renaissance style appeared for the first time in Sweden, with royal castles remodelled Kalmar being a fine example. Economically, Sweden remained mostly self sufficient, its few imports luxuries like cloth, wine and spices. With around 8000 inhabitants, Stockholm was its most important city, although Gothenburg was founded in 1607 to promote trade to the west. Gustavus Adolfus: the rise of the Swedish Empire During the reign of Gustavas II Adolfus Sweden became a European power. Though still in his youth he was considered able enough to rule, and proved so by concluding peace treaties with Denmark (1613) and Russia (1617), the latter isolating Russia from the Baltic and allowing the Swedes control of the eastern trade routes into Europe. In 1618 the Thirty Years' War broke out in Germany. It was vital for Gustavus that Germany should not become Catholic, given the Polish king's continuing pretensions to the Swedish crown, and the possible threat it could pose to Sweden's growing influence in the Baltic. The Altmark treaty with a defeated Poland in 1629 gave Gustavus control of Livonia and four Prussian sea ports, and the income this generated financed his entry into the war in 1630 on the Protestant side. After several convincing victories Gustavus pushed through Germany, delaying an assault upon undefended Vienna. It cost him his life. At the Battle of Liitzen in 1632 Gustavus was killed, his body stripped and battered by the enemy's soldiers. The war dragged on until the Peace of Westphalia in 1648. With Gustavus away at war for глисЬ of fiis reign, Sweden ran smoothly under the guidance of his friend and chancellor. Axel Oxenstierna. Together they founded a new Supreme Court in Stockholm (and the same, too, in Finland and the conquered Baltic provinces); reorganised the national assembly into four Estates of nobility, clergy, burghers and peasantry (1626); extended the university at Uppsala (and founded one at Abo modern Turku); and fostered the mining and other industries that provided much of the countrY's wealth. Gustavus had many other accomplishments, too: he spoke five languages and designed a new light cannon, which assisted in his routs of the enemy. The Caroleans The Swedish empire reached its territorial peak under the Caroleans. Yet the reign of the last of them was to see Sweden crumble. Following Gustavus Adolfus' death and the later abdication of his daughter Christina, Karl X succeeded to the throne. War against Poland (1655) led to some early successes and, with Denmark espousing the Polish cause, gave Karl the opportunity to march into Jutland (1657).