Final answer:
Richard Nixon's greatest achievements include détente with the Soviet Union and the establishment of the Environmental Protection Agency (EPA). Détente helped ease Cold War tensions and reduce the risk of nuclear war, while the EPA marked a major step towards environmental protection in the US.
Step-by-step explanation:
Richard Nixon's greatest achievements include his policy of détente with the Soviet Union and his establishment of the Environmental Protection Agency (EPA). Détente, which aimed to reduce tensions and improve relations between the US and the USSR, led to important arms control agreements, such as the Strategic Arms Limitation Treaty (SALT). This achievement was important because it helped ease Cold War tensions and reduce the risk of nuclear war. The creation of the EPA was significant because it marked a major step towards environmental protection and regulation in the United States, addressing issues such as pollution and conservation.