Games like Spirit Oath
Games like Spirit Oath include Kingdom Rush - Tower Defense, Total War: WARHAMMER III, Total War: WARHAMMER II, Shadow Tactics: Blades of the Shogun, and Bastion. We matched them by the tags players give Spirit Oath on Steam (Indie, Strategy, Action, Adventure, and RTS): closest matches first, and among equally close ones the better-known games.

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

Total War: WARHAMMER III
Shared: Strategy · RTS · Fantasy

Total War: WARHAMMER II
Shared: Strategy · RTS · Fantasy

Shadow Tactics: Blades of the Shogun
Shared: Strategy · Indie · Isometric

Bastion
Shared: Indie · Action · Adventure

Wolcen: Lords of Mayhem
Shared: Isometric · Action · Indie

The Witcher 3: Wild Hunt — Remastered
Shared: Adventure · Atmospheric · Fantasy

Brothers - A Tale of Two Sons
Shared: Adventure · Indie · Atmospheric

Shadow Tactics: Aiko's Choice
Shared: Strategy · Action · Isometric

GemCraft - Chasing Shadows
Shared: Strategy · Indie · Action

Kingdom Rush 5: Alliance TD
Shared: Strategy · Tower Defense · Indie

Orcs Must Die!
Shared: Strategy · Action · Indie

Orcs Must Die! 2
Shared: Action · Strategy · Indie

Kingdom Rush Frontiers - Tower Defense
Shared: Strategy · Tower Defense · Fantasy

Deathtrap
Shared: Action · Strategy · Indie

Kingdom Two Crowns
Shared: Strategy · Tower Defense · Singleplayer

Idle Champions of the Forgotten Realms
Shared: Strategy · Adventure · Indie

Tempest Rising
Shared: Strategy · RTS · Isometric

Rock 'N' Roll Defense
Shared: Strategy · Action · Indie

Infested Planet
Shared: Strategy · Action · Indie

Hollow Knight
Shared: Indie · Adventure · Atmospheric

Taur
Shared: Strategy · Action · Indie

SpellForce 3 Reforced
Shared: Strategy · RTS · Fantasy

Command & Conquer Red Alert™ 2 and Yuri’s Revenge™
Shared: Strategy · Action · RTS