 Complete the following phrase:  In the middle of the 17th century Sweden was the third-largest country in Europe by land area, surpassed by only Russia and Spain. Sweden reached its largest territorial extent under the rule of Charles X after the treaty of Roskilde in 1658, following Charles Xs risky but successful crossing of the Danish Belts. The foundation of Swedens success during this period is credited to Gustav Is major changes to the Swedish economy in the 16th century, and his introduction of Protestantism. In the 17th century, Sweden was engaged in many wars, for example with the PolishLithuanian Commonwealth, with both sides competing for territories of todays Baltic states, with the disastrous 