After world war 1 the United States wanted to isolate themselves from things like that because of how bad the war was. They went as far as to not join the league of nations that their President made himself with other presidents. After the Korean War, they decided to not isolate themselves and meddle as much as possible to prevent the spread of communism because it would strengthen the Soviet Union who was the main enemy.
<span>here
is archaeological evidence for human occupation before the land bridge
from Siberia opened up.
There has also been some recent DNA evidence
that suggests there might have been some European settlers before the
Vikings.
Although most of the DNA evidence points to Northern Asia. </span>
The army developed the military occupational specialty system for tracking the weaponry skills in WWII.
These MOS system had various fields like communications department, gunnery and gunnery control department, field and coast artillery, air crew, security departments etc.
The selected soldiers are assigned their specific tasks and all the groups are organised by a alphanumeric code system.
Volcanic activity , earthquakes , tsunamis.
The information found by Lewis and Clark showed many new places to settle, what the new land was like, and what could be accomplished in those areas. They found more land to farm and build homes. They also found some of the major rivers and landmarks of today.
