The Precambrian eon is separated from the Phanerozoic eon in the fossil record because of poorer record of fossils than that of the succeeding Phanerozoic eon.This is because many Precambrian rocks have been heavily metamorphosed,obscuring their origins,while others have been destroyed by erosion,or remain deeply buried beneath Phanerozoic strata.The Phanerozoic Eon covers 541 years to the present while Precambrian Eon covers 4.6 billion years.
United States did not like communism in the 50's and 60's. So they fought proxy wars with the U.S.S.R., now dissolved in to different countries.<span />
The two main arguments that opponents of annexing foreign territories
presented were 1) that it was too expensive and costly for the US to do
so, and 2) that it was morally reprehensible since it usually led to the
demise of local economies and civil rights.
It's called - Utopian Society