1. The savages who attacked Vincent;
2. The others who would attack/abduct 815 castaways;
3. The survivors of Flight 815; and
4. The submariners, a military group, that runs ashore at the outer reef.
All these groups have the following common traits:
1. The will to survive.
2. Territorial protection of the island.
3. The need to gather, store and consume necessary resources.
There are three basic grounds proposed in the guide:
1. The 815ers beach camp;
2. The jungle; and
3. A vast underground facility which would be found later in the series.
The inference is that the underground facility has been abandoned, so the castaways would move into it as their home base on the island. This also means one of two things: the facility had a prior island group that was wiped out (like the Dharma story line), or the Others abandoned their facility to live on the land.
I like the idea that the island has multiple groups competing against each other for survival. I like the idea of a band of island savages, a primal group that would seek to cut off expansion of any new group on their island. I could see this primitive group worshipping the smoke monster for protection.
The Others on the other hand are a mixed bag. They could be other people who shipwrecked on the island like the 815ers, which would put them into same mindset as the castaways (as allies). However, the story lines indicate that the Others would be attacking the castaways, so is this island group the remains of a failed scientific research facility, abandoned military outpost or some other group such as prisoners sent off to rot on a penal colony?
The submariners add the twist of adding a group with the actual means and skill set to leave the island with modern technology. It could be that they could team up with the 815ers to use the underground facility to manufacturer and repair the submarine for seaworthy rescue. Or, the submariners could be a trap to confine, enslave or wipe out all people on the island to reclaim it as their own secret base. As indicated earlier, we don't know who these military men are because the uniforms are different (leading to the possibility that they are even time travelers, for whose existence must be kept secret from the rest of the world.)
One could imagine the various branch story lines from the interaction between these groups. The 815ers and Others could be at odds, but there could be some castaways, led by Locke, who could splinter off and join the Others. Likewise, there could be some in the castaway group who would want to try to communicate, trade and find peace with the savages, especially as a means to acquire the island power to fight off the Others' attacks. The submariners could be the wild card, playing each group off each other to achieve their own goals.
The key to control of the island appears to be the underground facility. Whether it is functional, operational is an open question, but it would provide the best secured location on the island. Once it is found, it could lead to a siege by the other groups who want or need it.
