I realized that by converting as many wildlings as possible from the starting island, I could secure enough mana and power for battle even if the islands were not connected by land. This reduces the time it takes to prepare for the "Uplift" and build a boathouse, but it is difficult in that respect because it depends a lot on luck to gather wildlings from the surrounding islands.

Regarding the phenomenon of enemy missionaries gathering, I adopted this strategy because enemy missionaries sometimes gathered on the bridge connected by the "Uplift" when I placed a shaman in the position shown in the video.