Engulfed in the tremendous struggle to prevent the Civil War from dividing the Union between North and South, Abraham Lincoln was equally determined to prevent the seeds of separation from ever appearing in the vast American West.

Between the Mississippi River Valley and California lay a 2,000-mile emptiness known as "the Great American Desert." Lincoln was determined to bridge this unknown expanse and bind the West to the East with the same iron rails that had already done so much to link the Midwest and the Northeast.

Here, in this essay, New York Times bestselling historian Thomas Fleming tells the dramatic story of the building of the Transcontinental Railroad and Lincoln's little-told role in it.