Blood Harvest requires building Divine Sparks into tabletop games, and is a little-bit "gamey". Eternal Battle requires buying into a battleground where people kill each other and keep coming back from the dead. That's a bit on the bonkers side.
Compared to those two Homeland Invasion is a lot easier to "sell" to players. Not only do you not have to work at the concept, I also think it would easily work for non-Sundered Empire settings.
Here is the blurb from the start of the section:
The best thing about this is that, rather than being one scenario, it is actually seven scenarios. And there is a little bit of variety in the scenarios too.Chainmail Core Rulebook page 93 wrote:Homeland Invasion
Each of the seven scenario variants that follow depicts an attacker raiding deep into a defending faction’s territory. In a campaign game, the player with fewer victory points is the defender and the player with more victory points is the attacker. This scenario gives huge advantages to the defender,
taking the place of the support troops a player with a lower score normally gets against a player with a higher score (see Chapter 9: Running a Chainmail Campaign).
If you are not playing a campaign, randomly determine which player is the defender. The most satisfying way to play Homeland Invasion is to fight two skirmishes, one after the other, allowing both players to take a turn as the attacker and the defender. Alternatively, just play one game with the
stronger player as the attacker.
Each scenario description contains information on the environment, terrain, special rules, and victory conditions.
Essentially, if you play a Sundered Empire tabletop game and the PCs decide to attack a city belonging to an enemy faction, Homeland Invasion is a good way to start thinking about how to go about it.
There are some interesting "house rules" for each faction to use when resisting invasion. For example, Ahmut's Legion get a chance to animate dead, whenever a person is killed in a Homeland Invasion and Mordengard have their homeland defended by traps that their own troops can avoid.
It might be possible to add the Social Collapse Point System (from Night Below) to Homeland Invasion to make more of a longer campaign based on destroying a city.