Answer: D, The Civil War caused more American deaths than any other war.
Step-by-step explanation:
It cannot be A because multiple wars have lasted for longer than three years, such as WWI and WWII.
It cannot be B because wars, such as WWII, costed approximately $4 trillion, and the Civil War costed approximately $7 billion.
It cannot be C because the Revolutionary War with Britain was fought on American soil.
It must be D because all other options are incorrect. The Civil War had over 600,000 American deaths - the most of any American war.