Historians on America is a series of individual essays that selects specific moments, decisions, and intellectual or legislative or legal developments and explains how they altered the course of U.S. history.

Historians have used many lenses to analyze how historical change comes about. Thomas Carlyle, the 19th-century British writer, famously defined history as "at bottom the History of the Great Men who have worked there," and he saw heroic individuals as the drivers of change. In the 20th century, the French school of historians known as the Annales (for the journal where they published) reacted against Carlyle and other traditional historians who had presented history as largely a chronicle of wars and political events. In their quest for the roots of historical change, the Annales historians focused on the everyday lives of ordinary people in centuries long past.

Other recent historians have examined technology as a driving force or analyzed the effects of climate, natural resources, and environmental devastation. Under "theories of history," the online encyclopedia Wikipedia currently provides 121 listings.

In this book, we use a different lens – what might be called the tipping-point theory of history, a term borrowed from a recent best-seller in the United States written by the journalist Malcolm Gladwell.

"The – Tipping Point' – comes from the world of epidemiology," writes Gladwell. "It's the name given to that moment in an epidemic when a virus reaches critical mass. It's the boiling point. It's the moment on the graph when the line starts to shoot straight upwards." Gladwell adds, "One of the things I explore in the book is that ideas can be contagious in exactly the same way that a virus is."

Our premise in this book is that by analyzing a few tipping-point events, one can come to a better understanding of not only how the United States became the country it is today but of the values woven into this nation's fabric. From the viewpoint of the present, it is easy to forget that, just 200 years ago, the United States was a fledgling democracy, the recently liberated colony of a world power, with a backwoods economy based on agriculture and exploitation of its natural resources. It's also easy to forget that the institutions, ideas, laws, and values that govern the United States in the present were the creations of individual human beings in a specific set of circumstances.

We asked 11 historians, each an expert in his field, to consider a development that led to the creation of an idea or an institution that is central to America today. Most of the time, our authors find that a heroic individual plays a distinct role: George Washington's decision to retire from the first presidency after two terms guaranteed that the new nation would not have a king. The 1954 Supreme Court decision that led to racial integration of American schools is hard to imagine without Earl Warren as chief justice. The Marshall Plan, which helped bring relief to a devastated Europe after World War II, is certainly well named.

Yet it is also possible to see less personalized and less dramatic transformative events – laws passed by Congress, court decisions, the development of public schools – as examples of the tipping-point theory in action. They occur at times when an accretion of ideas, social movements, economic interests, and other forces have attained a critical mass. When looked at closely, many sudden transformations do not turn out to be sudden.

We do not mean to suggest that historical tipping points occur only in America, of course. By telling these American stories, we hope to provide ways for readers to view history, societies, and institutions in a new light of understanding.