[292] Fred I. Greenstein, in his journal article on Polk, noted that Polk "lacked a far-seeing awareness of the problems that were bound to arise over the status of slavery in the territory acquired from Mexico"[293] William Dusinberre, in his volume on Polk as slave owner, suggested "that Polk's deep personal involvement in the plantation slavery system ... colored his stance on slavery-related issues".[294]
Greenberg noted that Polk's war served as the training ground for that later conflict:

The conflict Polk engineered became the transformative event of the era. It not only changed the nation but also created a new generation of leaders, for good and for ill. In the military, Robert E. Lee, Ulysses S. Grant, Stonewall Jackson, George Meade, and Jefferson Davis all first experienced military command in Mexico. It was there that they learned the basis of the strategy and tactics that dominated the Civil War.