Sweden lost its grand power status through the Great Nordic War.

For the entirety of the 17th century, Sweden punched above its weight on the international arena. It was a sparsely populated country that was lucky in having a strong centralised government that could extract resources and wage war at a level above the average of Europe at the time.

In the Great Northern War 1700-21, Sweden faced Denmark-Norway, Russia, Poland-Lithuania, Saxony and eventually also Hannover and Lübeck and Brandenburg-Prussia. This proved to be too much even for Sweden, and the Swedish Empire broke under the strain, losing Ingria, Kexholm, Bremen, Estonia and Livonia in the war.

Karl XI, who died 1697, had created a fantastic semi-professional army which served his son, Karl XII very well throughout the war. Sweden won many spectacular victories with this army - Narva 1700, Düna 1701, Kliszow 1702, Fraustadt and Grodno 1706, Holowczyn 1708, Helsingborg 1710 and Gadebusch 1712. In no battle did this army face better than 1:1,25 odds, most often far worse.

As /u/cavetroglodyt say, the combination of fighting all these enemies, no allies, a crippling plague epedemic that broke out 1710 gutted the ability to raise new armies. Nevertheless, Sweden raised this army three times - 1700, 1710 and 1715.

/u/vonadler will probably be able to answer this in depth.

I was in Stockholm two weeks ago and the exhibition in the "Historiska Museet" mentioned a terrible pandemic and military losses to Russia as primary reasons. An answer that goes beyond that would be awesome.