When using the 2D board style, Invaders are grouped together by type and health, and there isn't space in all cases to also differentiate them by Strife. So for example, if one Town has Strife and another does not, they are not shown separately. To target a specific one for damage or another effect, press the Spirit Foresight button on the right, then press the land. A window will appear where you can select the Invader you want.

Alternatively, you can switch to the 3D board style, then switch back (in single player mode).