Simplify the following text for a Grade 2 native English-speaking person.
Original: It is the sixth installment of the Call of Duty series and the direct sequel to Call of Duty 4 : Modern Warfare , continuing the same storyline , with Call of Duty : Modern Warfare 3 set to end the storyline . It was released in conjunction with two other Call of Duty games : Call of Duty : Modern Warfare : Mobilized for the Nintendo DS , and Call of Duty : Modern Warfare : Reflex , a port of Call of Duty 4 adapted by Treyarch for the Wii console .
Simplified: It is the sixth game in the Call of Duty series .