“I sold a Napoleon letter yesterday,” remarked Howard Zerwitz. This kind of thing isn’t unusual for him, since Zerwitz’s American Historical Guild (AHG) provides historic autographs, documents, letters, and other artifacts to collectors around the world—all reflecting historic events. Zerwitz has sold letters and documents from every American president, as well as letters from people like Thomas Edison, Albert Einstein, and Mark Twain. In his niche Long Island business, Zerwitz has been dealing with pieces of history for some 40 years. Yet he wasn’t particularly drawn to history during his school days. His love for history, and his desire to preserve it carefully and accurately, has grown gradually—alongside his collections. Zerwitz works with documents and artifacts that begin in the $500 to $1,000 range, and increase in value according to their rarity and historical significance. He reports that his clients include small-business owners, doctors, teachers, police officers, and Fortune 500 …