On July 4, 1776, The American Continental Congress adopted a Declaration of Independence in Philadelphia, demanding freedom from British rule. Although Americans celebrate July 4th as their Independence Day, the months leading up to that day, and those that followed, were also critical to the nation's revolutionary cause. In a best selling new book called 1776 (published by Simon and Schuster), Pulitzer Prize winning historian David McCullough recalls the fateful year that transformed an army and gave birth to a nation.

David McCullough calls 1776 "the most important year in the most important struggle" in American history. He says that when the Revolutionary War began in 1775, the colonists were fighting for their rights as English men and women, not for independence. By 1776, there was talk of freedom in the air, but only about 1/3 of all Americans supported that notion, and prospects for achieving it looked slimmer by the day. "We were led by a general who had never commanded an army in his life before, George Washington, who was all of 43 years old," Mr. McCullough explains. "We lost every time we confronted the British, and very often it was Washington's fault. He had a lot to learn, but he always learned from his mistakes. But as the war progressed, every indication was that we had almost no chance to win."

As for the army Washington commanded, David McCullough says, don't picture men in uniforms, except for a few of the officers and the Commander in Chief. "They were farmers by and large," explains the author, "small tradesmen, carpenters, sailors, cobblers, all kinds of ordinary people of every race, color and nationality. Some were old men, some were as young as 14, 15 years old or younger."

Nor did they have much experience, if any, in fighting a war. "The British General Burgoyne called them 'rabble in arms' and that's what they looked like," says David McCullough. "At its maximum that year, there were probably 20,000 men, but there were always large numbers who were sick, and as winter came on, they had no winter clothing and began deserting. Many, when their enlistments were up -- and their enlistments were always very short -- would simply pack up and go home.

Mr. McCullough says that by the end of  December, George Washington had an army of maybe only 3,000 men, who were all in rags. "Many had no shoes. They were hungry, even starving," he says. "But they, like their commander would not give up."

In his book 1776, David McCullough follows America's changing fortunes over the course of that hard year. An early victory, when British troops were routed in Boston, was followed by a devastating defeat at the Battle of Brooklyn in New York. But that loss was offset by the Continental Army's daring escape across the East River. "They hadn't eaten for days," says Mr. McCullough. "They hadn't slept for days. And these people, under Washington, succeeded in escaping, without the single loss of a man -- 9,000 people, all of their equipment, cannons, horses, everything. It wouldn't have been possible except the wind kept the British from bringing their warships up into the East River, and a providential fog set in and covered the retreat when morning came and they still hadn't got everybody off."

But David McCullough believes it's also very important to understand that the Americans would never have gotten back across that river without the skilled mariners in their ranks -- fishermen and sailors who hailed mostly from Boston. "The Americans had shown there were some things they could do exceedingly well," says the author, "and gradually they would learn to fight what was the best professional army in the world."

That would start to become clear at year's end, when a desperate George Washington carried off a successful attack on an outpost at Trenton, New Jersey, manned by German mercenaries known as Hessians. It was a huge psychological boost for the troops and the public back home -- a victory David McCullough attributes both to the hard-won experience of 1776 and the innate character of George Washington.

"Washington was picked as the Commander in Chief by the Congress," notes Mr. McCullough. "They picked him not because he was a military genius -- he wasn't. "He wasn't a great orator like Patrick Henry. He wasn't an intellectual genius like Thomas Jefferson or John Adams. He was a leader, and he had the courage of a leader. And he would not quit. And he never forgot what the cause was about. And in the end, when the war was over, he would, as no conquering general ever had before, give back his command to the Congress. He turned away from power, and he would of course consequently become Commander in Chief in the full sense as President of the United States."

David McCullough says that by the end of 1776, American soldiers had shown that with ingenuity and perseverance -- one of George Washington's favorite words -- they could in fact "work wonders." "It would be a very long war," he notes. "It would last 8 ½ years before it was over. But this was the worst time. The last few months of 1776 were the darkest hours in the history of the United States of America, and when we celebrate 1776, we should never forget that it was only made possible by those men who were willing to follow Washington through hell, and did."

In writing 1776, David McCullough says he wanted to convey what it was like to have experienced the Revolutionary War, and to describe that experience in the words of the people themselves. "Particularly soldiers in the ranks" he adds, "farmers from Connecticut, a shoemaker named Joseph Hodgkins from Ipswich, Massachusetts, a young boy named John Greenwood, who wrote diaries or wrote letters or wrote memoirs, because I don't think you really know anything until you feel it."

David McCullough has testified before the U.S. Congress on the need to improve the way history is taught in American schools. He believes that too many of the nation's teachers lack adequate training in the subject, and that school textbooks often fail to convey the drama and humanity of historical events. Mr. McCullough's books, 1776 included, have won praise for doing just the opposite. Combining extensive scholarship with vivid storytelling, he breathes new life into people, both celebrated and forgotten, who shaped American history.