Complex sentence: That Task Force was based in Tikrit, and cooperated with 5 different Iraqi Army Divisions from Oct. of 2007 to Dec.2008, and during that period there was a significant decrease in insurgent activity in Iraq's four Northern provinces and the Kurdish area.
Split into simpler sentences: That Task Force was based in Tikrit, and cooperated with 5 different Iraqi Army Divisions from Oct. of 2007 to Dec.2008. During that period there was a significant decrease in insurgent activity in Iraq's four Northern provinces and the Kurdish area.