This book "", as the author states in his preface, ""is a study in public opinion."" As such it is an examination of propaganda methods and the manipulation of public opinion, and much good use is made here of newspaper editorials, Congressional records, and political speeches to provide a first-hand understanding of the evolution of the two opposed ""forces"" named in the title. While most of our attention is directed towards the Polk administration and the Mexican War, the birth and growth of the basic issues, from Jefferson's time and even earlier, are carefully outlined. The part played by expansionist sentiment later, in the causes of the Civil War, is also assiduously dissected, and the two final chapters are devoted to Manifest Destiny's last stand, the Spanish-American War, ""partly for (its) own take and partly to offer the reader helpful comparisons"" to the main body of material. Continentalism and Imperialism were at certain periods in our history real crusades; evoutly believed in; at other times they were weapons wielded cynically by various factions in their bids for supremacy; and all the different changes rung upon them are fascinating to follow. Fredrick Merk is an astute analyst who also has a talent for breathing life into the men and ideas of a century ago.