The period began about 10,000 years ago with the domestication of plants and animals.

I believe the answer you are looking for is the "Neolithic Period". 

Italian workers migrated to northern provinces

It is the doctrine that the us had the right and duty to expand throughout north america. it just means they believed they had the right to expand westward and they did! they stated with the 13 colonies and then they kept moving gaining different territories throughout the years