The correct answer is D. The achievement of Manifest Destiny and the need for a "New American Frontier". The Manifest Destiny was an american philosphy from the 19th century that stated it was America's right, given by God, to expand and conquer other territories. In this period, imperialism was increasing at a global level and United States didn't want to be left behind of this imperalist race. The idea of the <em>New american frontier</em> was to expand the settled area as the first americans had started to do when they got to the new continet. The frontier had actually been changed by events like the Louisiana purchase but there was always a new frontier they wanted to reach.
