Pioneer settlers were sometimes pulled west because they wanted to make a better living. The biggest factor that pulled pioneers west was the opportunity to buy land.
Manifest destiny was caused by the fact that the American people were historically connected to English civilization, this gave them a sense of superiority over the other peoples who lived in North America. Because of the fact that they were white and civilized, the Americans felt superior to the Indians.
Yes, it is true that caves are a type of island ecosystem according to the theory of island biogeography, since many caves at one point in time were in fact underwater.
