A Baltic Sea outlet was vital to Russia, but Sweden blocked the way. Without an access to the sea, Russia could not develop effectively, and its commerce with Western Europe was impossible. In 1700 Tzar Peter I stated a disrespectful treatment during his visit to Riga and declared war to Sweden. Russians strove for recovering previously lost territories of Karelia and Ingermanland. Saxony, Denmark, and Poland also had territorial ambitions and supported Russia. The war began favorably to Sweden - they managed to crush Saxon and Danish forces. In autumn of 1700 the Russian army of 40,000 soldiers lead by Tzar Peter besieged the Swedish fortress Narva. Swedish King Karl XII advanced to assist the garrison. He attacked and smashed Russian forces. Tzar Peter learnt a lesson from this disreputable defeat and undertook forming a new regular army of European type. In 1701 Swedes invaded Poland, enthroned their loyal king Stanislaw Leszczinnsky, and made the country their new ally. By that time Russians managed to form the new army. They initiated a campaign, and in 1704 gained Narva that was one of the main defensive centers of Baltic lands. Karl XII never considered Russia an adequate opponent and decided to finish it once and for all. In summer of 1708 he detached a well-trained army of 60,000 to Moscow. However, their martial luck has let Swedes down. In September of 1708 Russians smashed the Leeuwenhaupt's corps in the battle of village Lesnaya. The anti-Moscow campaign failed. Hoping to capture provisions, Swedes invaded Ukraine, where the ex-adherent of Russia Hetman Mazepa joined them. However, the Swedish Army failed again. Russians left Swedes behind and gained the Hetman's quarters of Baturin City with the main food storehouses. In spring of 1709, forces of Karl XII besieged Poltava, and the decisive battle broke out. Russians enjoyed a significant numerical superiority of 45,000 soldiers against 22,000 of Swedes. And again, the Swedish assault of Russian fortified line failed. The battle of Poltava was the turning point of the war that came to end with Russian triumph in 1721. Russia consolidated its grip on the Baltic shore.