If Invaders do extra damage in a land where all Invaders have Strife, what happens?

If Invaders do extra damage in a land where all Invaders have Strife, what happens?

Changed answer (as of Jagged Earth): The damage boost does not apply. (JE, p. 7) Per-land damage boosts only apply if the Invaders manage to muster up at least 1 Damage prior to Defend, so empty lands which manage to Ravage, lands where all Invaders are Strifed, or lands full of Explorers that are affected by Mesmerized Tranquility don't get per-land damage boosts. This is a change from pre-Jagged Earth, as noted on the JE rules p. 7.
If you wish to play with the old rule, you can, but the game will be harder.