 Complete the following phrase:  Following a series of conflicts between Poland and Sweden in 160011, 161718 and 16211625, all of which ended in a stalemate, Gustavus Adolphus invaded in 1626 to gain control over Livonia and relinquish Sigismunds claim to the Swedish crown. Sigismund, already in advanced age, continued his long-term ambition to seize Sweden, which gave Gustavus Adolphus a reasonable casus belli and justification for war. Though the Polish army achieved major victories in the previous battles against Sweden, particularly at 