What is Manifest Destiny in the United States?

How have America's racial doctrines contaminated our debate? What is "Anglo-Saxonism"? What is "Manifest Destiny"? How did the United States develop an ideology that combined religion and science to justify its advancement and dominance over Latin America? Is there a "White Man's Burden"?
For these questions we will discuss an excerpt from Reginald Horsman's work "Race and Manifest Destiny: origins of racial Anglo-Saxonism in the United States".