I just hope they provide an English translation so that we know what the hell they are singing about.
Here's some info at least, based on the song titles (it's pretty obvious what they refer to if you know Swedish history):
"Lejonet från Norden" means "Lion of the North" and refers to
Gustavus Adolphus who is considered to be the "founder", or at least the first king, of the Swedish Empire. He was very successful, but died in battle in Germany during the
Thirty Years' War, the end of which I assume the song title "1648" refers to.
"En livstid i krig" means "A Lifetime in War". "Karolinens bön" means "Prayer of the
Carolean".
The title track "Carolus Rex" refers to king
Charles XII, like Gustavus Adolphus one of Sweden's most famous kings. He was also very much a war king, so much so that he was usually portrayed in military uniform rather than the usual royal 17th/18th century clothes. He was quite successful, but eventually he lead Sweden to a massive defeat against Russia in the city of Poltava (hence the song "Poltava"), which was pretty much the end of the Swedish Empire.
"Ett slag färgat rött" means "A Battle Colored Red". "Konungens likfärd" most likely refers to when they carried the dead Charles XII's body home from Norway, where he was killed in battle.
That's a short summary.