Final answer:
The United States ended World War II by dropping nuclear bombs on the Japanese cities of Hiroshima and Nagasaki, forcing Japan to surrender and thus avoiding a potentially lengthy and costly invasion.
The correct answer is option c. nuclear bombings
Step-by-step explanation:
The method the United States used that effectively ended World War II was through the use of nuclear bombings. This decisive action was taken with the dropping of atomic bombs on the Japanese cities of Hiroshima and Nagasaki. The rationale behind the use of the atomic bomb was to bring a quick end to the war and to force a Japanese surrender, thus saving Allied lives that would have been lost in a full-scale invasion of Japan.
While the use of the atomic bomb succeeded in its goal of ending the war, it remains a highly controversial decision due to the significant loss of life and ethical considerations surrounding its use on civilian populations. Prior to this decision, various measures such as diplomatic talks, economic sanctions, and military blockades had been employed, but none brought the conflict to a definitive close.