Well there are no options, but I would say the 13th amendment, it abolished slavery.
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<span> Military spending that began in 1940 to bolster the defense effort gave the nation’s economy the boost it needed, and millions of unemployed Americans returned to work to make the weapons of war needed to protect the United States
hope this helps
(that is answer)</span>
"President Nixon believed his Vietnamization strategy, which involved building up South Vietnam's armed forces and withdrawing U.S.troops, would prepare the SouthVietnamese to act in their own defense against a North Vietnamese takeover and allow the United States to leave Vietnam with its honor intact." -Google
"Henry Kissinger signs the Paris Peace Accords on Jan. 27, 1973 in Paris. The war ended on April 30, 1975, when Saigon surrendered almost without fighting to the communist forces, ending the United States’ involvement in Vietnam.*" - https://slate.com/human-interest/2014/11/why-did-america-lose-the-vietnam-war.html
Steak engine made water power obsolete
