You have probably never read this in history books but pigs and earthworms helped Europeans defeat the Native Americans. (Horses and cows too.) Malaria and other diseases helped quite a bit as well, but that is another story. (This came from reading the book 1493 which the prior post was also about.)
The first English settlers who came to Jamestown came from a land of neatly tended farms. When they came to the Chesapeake and other areas along the East Coast they saw wilderness. It was actually anything but.
First, a lot of the land was more densely settled than in England or other parts of Europe. The forests were managed and had been for centuries by regular fires being set to reduce the underbrush. This made hunting and travel much easier. Early Englishmen said the forests looked like English parks. Later the forests became overgrown with underbrush / understory growth as the Europeans disrupted Native American life.
Earthworms to the Attack
There was also a good thick layer of leaf litter. This becomes important because as that decayed it fertilized the trees and other plants. However, when earthworms were introduced by the Europeans, (almost certainly it wasn’t planned, it just happened) they had a dramatic effect. They are apparently very efficient at eating through leaf litter and leaving their droppings. So the layer of leaf liter was quickly reduced and the soils were no longer as rich for the trees or the food crops.
Varying Farming Practices
The Native American “fields” didn’t look like what the Europeans knew and therefore didn’t appreciate them. This was because the fields weren’t monocultures. They consisted of maize, beans and squash growing together.
The beans would grow up the maize and the squash would spread along the ground and protect the roots.
There was also a lot of marsh lands and a plant (called hopniss?) that grew in abundance there had edible tubers. They didn’t taste as good as the Native Americans’ other foods but it was available when those were least abundant and kept the Indians from starving in bad times.
The Europeans looked to alter the landscape to fit their way of life and changed the landscape so there were fewer marshes. Therefore less of the hopniss.
Pigs on a Flanking Attack
But the coup de grace were the farm animals. Many got loose and went wild, especially the pigs. All of them would wander through the Native American fields of maize, beans and squash and either eat them or damage them. The pigs did this but even worse, it turns out that pigs love hopniss (or whatever the plant’s name was) and decimated the areas that the Native Americans had depended on.
Because of these changes, the land could no longer support as many people. Many had also died from European diseases. So many Native Americans pulled up root and headed west without being directly forced to do so.