The Swedish Empire was a major European power from the early 17th century to the early 18th century. It expanded significantly during the Thirty Years' War, gaining territories in Finland, Estonia, Latvia, and parts of Germany. The empire was known for its military strength and innovative tactics, particularly under the leadership of King Gustavus Adolphus. At its height, the Swedish Empire was one of the largest in Europe, influencing politics and trade in the Baltic Sea region. However, it began to decline after the Great Northern War (1700-1721), which resulted in significant territorial losses and marked the end of Sweden's status as a great power.