What Was "Oregon Fever," and How Did It Come About

What was "Oregon fever," and how did it come about?

A) It referred to the sense of idealism Americans had toward the West due to its portrayal in popular culture, although very few Americans actually made the journey as the government outlawed it.
B) It referred to a terrible outbreak of cholera that spread all the way east due to the cramped living conditions of groups of pioneers traveling to Oregon and other western territories.
C) It referred to the warmongering directed toward the Oregon area and the recruitment of American soldiers, as the French were the last obstacle standing in the way of American western settlement.
D) It referred to the panic the general American public felt at the prospect of further western expansion, due to widespread economic decline caused by the relocation of workers and industry.
E) It referred to the large migration of many settlers to Oregon, drawn there by the fertile land and eventually the federal government's promise of free land in exchange for four years of work.