The foundation of Sweden's success during this period is credited to Gustav I's major changes on 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 Polish–Lithuanian Commonwealth with both sides competing for territories of today's Baltic states, with the disastrous Battle of Kircholm being one of the highlights. One-third of the Finnish population died in the devastating famine that struck the country in 1696. Famine also hit Sweden, killing roughly 10% of Sweden's population.