Question

1. What does O’Sullivan suggest Americans should be able to possess by right of Manifest Destiny? 2. What reasons does he give?

Answer 1

Here are the answers to the given questions above.
1. John O'Sullivan suggests that Americans should be able to possess by right of Manifest Destiny is to overspread and to acquire the entirety of the continent which the Almighty has provided them for the development of the great experiment of liberty and the democratic government invested to them. 
2. The reason he gives is that it is for the full expansion of its principle and destiny of growth.
Hope this answer helps.

Answer 2

According to John O’Sullivan, newspaper editor who coined the phrase Manifest Destiny in 1848, Americans had the divine mandate to expand throughout and possess North America. He uses a religious justification to support this expansionist idea. In O’Sullivan’s view, Americans should expand westwards and possess these territories not only because it was obvious (manifest) but also because they had been chosen by God (they were destined) to expand westward and spread their traditions and institutions, while at the same time enlightening the less civilized nations.