Adolphus succeeded the throne at age 17 as Gustavus II when Sweden was at war with Denmark, Poland, and Russia. He created the most modern army in Europe by making military service obligatory for peasants.

After winning these wars he led an army into Germany to fight Roman Catholic domination. He saved North German Protestantism by destroying the Imperial army in the battle of Breitenfeld (1631).

Thereafter he crossed Thuringia and Franconia where the Protestant population welcomed the Swedish king. He defeated Wallenstein at the battle of Luetzen (1632) and was killed in action.