Games like Defender's Dynasty
Games like Defender's Dynasty include Thronefall, Stronghold: Definitive Edition, Stronghold Crusader: Definitive Edition, Kingdom Two Crowns, and Stronghold HD (2012). We matched them by the tags players give Defender's Dynasty on Steam (Strategy, City Builder, Tower Defense, Action, and Base Building): closest matches first, and among equally close ones the better-known games.

Thronefall
Shared: Strategy · Tower Defense · City Builder

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

Stronghold Crusader: Definitive Edition
Shared: Strategy · City Builder · Medieval

Kingdom Two Crowns
Shared: Tower Defense · City Builder · Strategy

Stronghold HD (2012)
Shared: City Builder · Real Time Tactics · Medieval

Age of Empires II (Retired)
Shared: Strategy · Medieval · City Builder

They Are Billions
Shared: Strategy · Base Building · Tower Defense

Age of Darkness: Final Stand
Shared: Tower Defense · Strategy · Action RTS

Kingdom Rush 6: Genesis TD
Shared: Strategy · Tower Defense · Action

Stronghold Crusader HD (2012)
Shared: City Builder · Strategy · Medieval

Becastled
Shared: Strategy · City Builder · Base Building

Bee Island
Shared: Strategy · Tower Defense · City Builder

Farthest Frontier
Shared: City Builder · Strategy · Medieval

Border Pioneer
Shared: Strategy · Tower Defense · City Builder

Kingdom Rush - Tower Defense
Shared: Strategy · Tower Defense · Action

Mindustry
Shared: Tower Defense · Base Building · Strategy

The King is Watching
Shared: Tower Defense · Base Building · Strategy

Manor Lords
Shared: Strategy · City Builder · Base Building

Kingdom Rush Origins - Tower Defense
Shared: Strategy · Tower Defense · 2D

DG2: Defense Grid 2
Shared: Strategy · Tower Defense · Action

Diplomacy is Not an Option
Shared: Medieval · Base Building · Strategy

Prison Architect
Shared: Strategy · Base Building · City Builder

Frostpunk
Shared: City Builder · Strategy · Base Building

Foundation
Shared: City Builder · Strategy · Medieval