3.990 years is about half as long as The Revolutionary War (American)
In other words, it's 0.4762 times the length of The Revolutionary War (American), and the length of The Revolutionary War (American) is 2.1 times that amount.
(a.k.a. American War of Independence) (1775-83) The War between Great Britain and the its thirteen colonies in North America (now the United States) for the independence of the United States is generally considered to have started with the Battle of Lexington and Concord on April 18th, 1775 (sometimes known as "The Shot Heard 'round the World") and to have concluded with the signing of the Treaty of Paris on September 3rd, 1783 — 8.3780 years. A total of 25,000 Americans are estimated to have died as a result of the war.