Stress does increase the risk of disease because it alters with ones brain and nerves which can lead to deadly diseases.
Exposed them to new lands to conquer as well as spread influence too. It allowed competing countries to appear superior if they conquered land in the land. Land=resources and power all equate to more economic oppurtunities
The Mississippi River was a long trail of flowing water. Erie Canals were made to be long and help water travel to help crops and plants grow. Hope I helped! :)