A collapsing world in 395 AD
Total War: ATTILA drops you into 395 AD, at the dawn of the Dark Ages, where famine, disease and war are already tearing things apart. A new power is gathering on the eastern steppes with a huge mounted host behind it, and its war king has his eyes on Rome. You pick a faction and play it through a campaign map that moves one turn at a time: manage provinces, politics, the family tree, civic matters and technological progress, then fight your battles out in real time as troops on the field. The period detail runs through the whole thing, with era-specific technologies, arms, religions, cultures and social upheaval shaping what you can do.
Playing it with friends
The game supports online co-op and online PvP, so a group can either work together on a shared campaign or take each other on. In co-op you split the work of running a faction across the map, coordinating moves turn by turn, and then handle the real-time battles as a team. In PvP the same campaign structure turns into a contest between players. Either way the loop is the same: plan on the campaign map, then command the fight when armies meet.
Survival is the core challenge
This is a survival-strategy game before it is a conquest game. Playing as the Western Roman Empire you start with vast territories but political in-fighting and enemies on every side, so holding what you have is the hard part. Fire is a real weapon: buildings can be set ablaze to terrify defenders, and the raze mechanic lets you wipe cities and regions from the campaign map entirely. Expect a grim, heavy atmosphere built for scale and ruin rather than comfort, and go in ready to defend rather than expand.