Answer:
the U.S. had withdrawn all its troops, the fighting in Vietnam. South Vietnam officially surrendered to North Vietnam on April 30, 1975.
Russia and Britain both gained partial control of Persia's economy.
Two mountain ranges, the Alps and the Apennines, helped to protect Rome from invasion. The Apennines divide the Italian peninsula in half and, according to SPQR Online, allowed the Romans to mass forces for counter-attack whenever they were threatened.
Http://www.amazon.com/Empire-Cotton-A-Global-History/dp/0375414142
