Games like Warlords Under Siege
Games like Warlords Under Siege include Against the Storm, Stacklands, Manor Lords, Thronefall, and Farthest Frontier. We matched them by the tags players give Warlords Under Siege on Steam (Action Roguelike, Action RTS, Wargame, Roguelite, and City Builder): closest matches first, and among equally close ones the better-known games.

Against the Storm
Shared: City Builder · Building · Base Building

Stacklands
Shared: Roguelite · City Builder · Survival

Manor Lords
Shared: City Builder · Building · Base Building

Thronefall
Shared: City Builder · Action RTS · Medieval

Farthest Frontier
Shared: City Builder · Building · Medieval

Frostpunk
Shared: City Builder · Survival · Building

Cities: Skylines
Shared: City Builder · Building · Moddable

Cult of the Lamb
Shared: Action Roguelike · Roguelite · Base Building

Prison Architect
Shared: Building · City Builder · Base Building

Workers & Resources: Soviet Republic
Shared: City Builder · Building · Base Building

Kingdom Two Crowns
Shared: City Builder · Building · Medieval

Foundation
Shared: City Builder · Medieval · Building

RimWorld
Shared: Survival · Base Building · Moddable

Dwarf Fortress
Shared: City Builder · Base Building · Building

Megabonk
Shared: Action Roguelike · Roguelite · Survival

Becastled
Shared: City Builder · Building · Medieval

Age of Darkness: Final Stand
Shared: Action RTS · Base Building · RTS

They Are Billions
Shared: Base Building · City Builder · Survival

Empires of the Undergrowth
Shared: City Builder · Building · Base Building

Bad North: Jotunn Edition
Shared: Wargame · Action Roguelike · Survival

Stronghold: Definitive Edition
Shared: City Builder · Building · Medieval

Banished
Shared: City Builder · Survival · Medieval

Medieval Kingdom Wars
Shared: City Builder · Medieval · Action RTS

Settlement Survival
Shared: City Builder · Building · Survival