Final answer:
General George Washington played the key role in foiling the Newburgh Conspiracy by appealing to the officers' loyalty and patriotism in 1783.
Step-by-step explanation:
The decisive role in foiling the Newburgh Conspiracy was played by General George Washington. The Newburgh Conspiracy was a potential military coup by the Continental Army in 1783, stemming from their frustration with Congress over unpaid salaries and pensions.
Washington defused the situation by addressing the officers in a meeting on March 15, 1783, appealing to their loyalty and patriotism, and urging patience, which led to the dissipation of the conspiracy.