The author's attitude towards westward expansion is ______.

A．It is altruistic.
B．Americans believed that they should bring freedom and democracy to the unfortunate people.
C．It reflects American's deep-rooted racism.
D．Amercans believed that their system would do benefits to others.

A．half of the population lived to the west of Appalachian Mountains
B．Americans had long been desirous of new territories
C．westward expansion was a solution to the conflicts between the two parties
D．America's industry was highly developed