George Washington and his Continental Army were facing defeat in the Revolutionary War in December of 1776. After losing Long Island and New York City earlier in the year, he had been retreating through New Jersey. By December, the men in the Continental Army were cold, hungry, tired of the long retreat. They were ready to go home when their enlistments were up at the end of December. At this point, Washington took a huge gamble. On Christmas night he and his troops crossed the Delaware River. On the morning of December 26 he routed Hessian troops fighting for the British at Trenton. Washington was victorious at this battle. On January 3, 1777, he met British troops at Princeton where he again was victorious. He then wintered in Morristown, New Jersey. These two small victories raised the spirits of the Americans and kept them fighting. All the British had to show after nearly a year of fighting was control of New York City.
Morale is a very important thing in a war. It is important both for the people fighting the war and for the political will of the people who are supporting the war. We saw the importance of morale of both sorts in the Vietnam Era.
I believe that the Battle of Princeton boosted morale of both sorts. It helped cause American men to be willing to enlist or remain enlisted in the army. Perhaps more importantly, it convinced both Americans and the French that the patriots could win the war and deserved support. Both of these factors gave momentum to the patriot side.