Total War battles broadly come in two flavors, and each has familiar dynamics. There's the siege battles, where one army storms the battlements of another, and there's the open field battle, where two armies maneuver and clash across a map until one is finally routed. With Total War: Warhammer 3, developer Creative Assembly is continuing the series' interweaving of narrative set-pieces with a special new kind of battle, the Survival Battle. To be reductive, it's Total War-meets-Tower Defense but that really undersells how engaging and how different the battle type is compared to what we've gotten used to in Total War games.
This is a companion discussion topic for the original entry at https://www.vice.com/en_us/article/jg8mgd/the-new-hybrid-tower-defense-tactics-mode-of-total-war-warhammer-3