Billed as the largest Civil War conference ever, it included educational sessions with more than 30 noted speakers, field sessions at Civil War sites and the Hagerstown-based preservation group's 10th anniversary banquet.
More than 400 people attended the brunch send-off event, which included talks by Gallagher and Pulitzer Prize-winning author James M. McPherson.
Gallagher - the author or editor of many Civil War works, including "Lee the Soldier" and "The Confederate War: Popular Will, Nationalism and Strategy" - challenged the assertion by a growing number of modern scholars that the South should have waged a guerrilla war.
While it's tempting to apply lessons from one era to another, it's dangerous because it usually doesn't work, said Gallagher, who said many people are wrongly looking at America's experience in Vietnam for a comparison.
You have to look at the beliefs, words and actions of the people of the time, he said.
In that case, it's not realistic to suppose white Southerners would have supported guerrilla warfare for a number of reasons.
For one, it would have required them to shun the majority of their leadership - trained in the West Point tradition - at a time when, fearful of slave uprisings, they were facing invasion from the North, Gallagher said.
Also, battlefield victories were important to build both national cohesiveness and morale among Confederates and support from potential European allies, he said.
McPherson, an American history professor at Princeton University and author of the prize-winning "Battle Cry of Freedom: The Civil War Era," chose religion and its effect on soldiers on both sides for his topic.
"I thought it was an appropriate subject for a Sunday," said McPherson, who said the soldiers' religious fatalism and almost-literal belief in life after death helped them face possible death.
Although the prospect of death tends to make soldiers in any war more religious, the Civil War armies were probably the most religious in American history because they were the products of the Second Great Awakening for Protestantism, he said.
It was a thrill to learn Gallagher was the surprise speaker, especially with McPherson on the same program, said Robert Delcamp, a music professor from the University of the South in Sewanee, Tenn.
Gallagher picked a very interesting topic, said Delcamp, who said he enjoys the "what ifs" of historical debate.
The mystery speaker's identity was no surprise to Frank Wild of Cheshire, Conn., who guessed it was Gallagher from the roster of speakers listed in the conference program and brought along nine of his books to have autographed.
Seeing Gallagher and McPherson speak back-to-back was a fitting ending to an impressive weekend, said Wild, who said he taped Gallagher's speech to listen to on his 51/2-hour drive home.
Between the number and caliber of speakers and the friendliness of the people, Wild said the conference was by far the best of all the Civil War conferences he'd ever attended.