The author is making a cultural allusion, therefore comparing the character to something in our present day culture. I hope this will guide you towards the right answer.
Manifest Destiny said that the United States had the right to expand to the Pacific Ocean. In 1845 the United States annexed the Republic of Texas and won de facto independence from Mexico. So the United States thought the could control the area since they won it. But the people in Mexico had just won independence so they did not want another ruler.
<span>Because he and other people began to worry about the future of the United States and thought it would lose the respect of its own citizens and of other countries.</span>