A Baltic Sea outlet was vital to Russia, but Sweden barred the way. Without any access to the sea, Russia could not develop effectively and commerce with western Europe became impossible. In 1700, Tsar Peter I claimed that he had been treated disrespectfully during his visit to Riga and declared war on Sweden. Russia strove to recover the previously lost territories of Karelia and Ingermanland. Saxony, Denmark and Poland also had territorial ambitions and supported Russia. The war began favourably for Sweden - they managed to crush the Saxon and Danish forces. In the autumn of 1700, the Russian army of 40,000 soldiers led by Tsar Peter besieged the Swedish fortress of Narva. Charles XII, the King of Sweden, advanced to assist the garrison. He attacked and crushed the Russian forces. Tsar Peter learnt a lesson from this disreputable defeat and undertook to form a new regular army in the European style. In 1701, the Swedes invaded Poland, enthroned the loyal king Stanislaw Leszczinnsky and made the country their new ally. By that time the Russians had created their new army. They initiated a campaign and in 1704 captured Narva, one of the main defensive centres of the Baltic lands. Charles XII never considered Russia to be a real opponent and decided to finish it once and for all. In the summer of 1708, he detached a well-trained army of 60,000 to Moscow. However, luck let the Swedes down. In September 1708, the Russians crushed the Leeuwenhaupt corps in a battle at the village of Lesnaya. The campaign against Moscow failed. Hoping to capture provisions, the Swedes invaded Ukraine, where they were joined by former Russian ally Hetman Mazepa. However, the Swedish Army failed again. The Russians left the Swedes behind and gained the Hetman's quarters in Baturin City which held the main food supplies. In spring 1709, forces of Charles XII besieged Poltava and the decisive battle broke out. The Russians enjoyed a significant numerical superiority of 45,000 soldiers against 22,000 Swedes. Again, the Swedish assault of the Russian fortified line failed. The Battle of Poltava was the turning point of the war that ended with the Russian victory in 1721. Russia consolidated its grip on the Baltic shore.