Total War is 15 years old. Creative Assembly has released a video to celebrate that fact. It's a round-up of scenes from the history of the series. It also briefly suggests something new, which, based on previous revelations, is likely a Warhammer game.
Total War: Warhammer was prematurely revealed in a Total War art book. While still not officially announced, it's almost certain that that's what the video's teaser is about. At around 2:32 a purple haze is revealed, and an inhuman roar echoes.
From the video's description:
"2015 will be our biggest year yet, and this latest trailer will give you a hint of what’s to come. Digital and tablet title Total War Battles: KINGDOM, 10v10 team strategy in Total War: ARENA, and more..."