The sentence that describes the main idea of Manifest Destiny is the one that says 'Americans had the right to expand their control across the continent'.
<u>Explanation:</u>
Manifest Destiny was a philosophical belief that took deep roots in the 'eighteenth century' among the newly settled Americans which led them to believe that it was there right to establish their prowess over the continent of 'North America' and bring the entire continent under their control irrespective of what the 'original inhabitants' of the continent thought.
They believed that the action of governing the entire continent was bestowed upon them as a responsibility by God himself.
