Concept of manifest destiny was based on expansionism.
Step-by-step explanation:
Manifest destiny was started during 19th century in US by John O' Sullivan , he was a journalist by profession. The people believed that the country's main aim was to expand. The main idea behind Manifest destiny is to capture more land that will be beneficial for cultivation purpose mainly the people focused in cotton cultivation and this would spread slavery to these parts as well.
The effect was that it included expansion of westward portion of the United States as well as there was increase in tension regarding political interests between Northern and Southern parts.
Various drawback was there, they are as follows, There was increase in slavery, It is unconstitutional by nature, many people died as well as suffered specially Indians, war and conflicts took place.