Essentially, the Nixon Doctrine was Richard Nixon's foreign policy manifesto. It outlined that the United States would provide help to foreign nations combatting communism with financial aid rather than military aid. This essentially was to limit the deployment of US military abroad, like in Vietnam or Korea.
The Nixon Doctrine was in line with Nixon's idea of "Detente" which literally means "relaxation" in French. Nixon wanted to defuse relations with China and the USSR by withdrawing US troops from "proxy wars" (wars fought between two opposing sides but either side is backed by a foreign power, in this case the United States and the USSR).
To answer the final part of your question, the Nixon Doctrine had initial success. The Doctrine was intrinsic to the Paris Peace Conference in 1973 which saw the end to the Vietnam War. It also allowed Nixon to obtain the Strategic Arms Limitation Treaty (SALT) with the USSR, which limited the amount of nuclear missiles (ICBM's especially), and become the first US President to visit Communist China. The Doctrine was essentially a part of a plan for "peaceful coexistence" between the democracies and the communists, and may have been successful were it not for Nixon's downfall in 1974 and Ford and Carter's lack of continuity in the Doctrine.
Hope I helped and please rate my answer :)
He wanted to use the Mississippi for trade
Answer:
People, Environment , and patterns seems to be correct
Im guessing they were called "wagon trains". Apologies if i'm incorrect!
C. Democrats.
The rest do not work in this time period.
