The most important purpose of irrigation was to

preserve scarce water supplies.
provide transportation routes.
share water with neighboring peoples.
keep farmers from growing food surpluses.

nativists tried to get rid of the immigrants as they thought they were going to ruin the u.s.  

. political or economical policy that isolates a country from participating in international relationships. it has been suggested that the united states participates in isolationism because of its lack of involvement in particular wars or alliances.