In her book 'Manifest Destiny' author Amy Greenberg shows the background and political context, society and cultural conditions that bred a new ideology called 'Manifest Destiny' which became a driving concept in the history of America. Referring to historical source materials such as primary documents, Amy Greenberg considers how the ideology developed from the roots of colonialism to become a political theory in its own right in the 1840s as a method for pushing beyond America's borders towards the Pacific ocean.
She shows the process and ideology of the territorial expansionist motivation of America and how its colonial beginnings provided a natural field for the growth of such ideas of expansion and it's eventual evolution into a full blown policy 'Manifest Destiny.' Its foundation idea was that America had almost a God-given right to grow across the North to the coasts. So this 19th-century doctrine that the expansion of the United States throughout the American continents was both justified and inevitable grew and became accepted at the time. Eventually opinion became entrenched and during the 19th century a period of American expansion continued under the belief that America could and should cover from coast to coast. This belief helped encourage western settlement, Native American land removal and the war with Mexico.