This seems to work. See the MW API at wikipedia.

Wikipedia pages on Category:Civilization_(series)

DEBUG - Data structure retrieved =

stdClass Object
(
    [batchcomplete] => 
    [query] => stdClass Object
        (
            [categorymembers] => Array
                (
                    [0] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization (series)
                        )

                    [1] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization (video game)
                        )

                    [2] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization II
                        )

                    [3] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization II: Conflicts in Civilization
                        )

                    [4] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization II: Test of Time
                        )

                    [5] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization III
                        )

                    [6] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization III: Conquests
                        )

                    [7] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization III: Play the World
                        )

                    [8] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization IV
                        )

                    [9] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization IV: Beyond the Sword
                        )

                    [10] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization IV: Colonization
                        )

                    [11] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization IV: Warlords
                        )

                    [12] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization V
                        )

                    [13] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization V: Brave New World
                        )

                    [14] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization V: Gods & Kings
                        )

                    [15] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization VI
                        )

                    [16] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Avalon Hill's Advanced Civilization
                        )

                    [17] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Baba Yetu
                        )

                    [18] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization (2002 board game)
                        )

                    [19] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization (2010 board game)
                        )

                    [20] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization: Call to Power
                        )

                    [21] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Call to Power II
                        )

                    [22] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization: The Card Game
                        )

                    [23] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization: Beyond Earth
                        )

                    [24] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization: Beyond Earth - Rising Tide
                        )

                    [25] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Sid Meier's Colonization
                        )

                    [26] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Deus (board game)
                        )

                    [27] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Music in the Civilization video game series
                        )

                    [28] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization Revolution
                        )

                    [29] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization Revolution 2
                        )

                    [30] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Rhye's and Fall of Civilization
                        )

                    [31] => stdClass Object
                        (
                            [ns] => 0
                            [title] => CivCity: Rome
                        )

                    [32] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Sid Meier's Alpha Centauri
                        )

                    [33] => stdClass Object
                        (
                            [ns] => 0
                            [title] => Civilization World
                        )

                )

        )

)