Complex sentence: This season Huddinge and Arboga had to play in the qualification series to stay in the league, but Arboga decided not to play because of their bad economic state of affairs, so they joined Division 1 in the 2007--08 season.
Split into simpler sentences: This season Huddinge and Arboga had to play in the qualification series to stay in the league, but Arboga decided not to play because of their bad economic state of affairs. This meant that Arboga joined Division 1 in the 2007--08 season.