Americans believed expansion would offer new economic opportunities. this perception is known as

Americans believed expansion would offer new economic opportunities. This perception is known as Manifest Destiny.

Explanation:

Manifest Destiny was a 19th-century American belief that the United States was destined to expand across the North American continent.

The term was first coined by journalist John O'Sullivan in an anonymous article published in 1845 by The United States Magazine and Democratic Review, in which he defended the fate of "allowing" the United States to expand across the continent and allow a growing nation to develop freely.  

During the Mexican-American War and later, the term was used to justify the annexation of the western territories of Mexico (Arizona, Texas, California, etc). On the eve of the Spanish-American War, the term was revived by the Republicans to give a theoretical justification for the US foreign expansion.

The term has ceased to be widely used in politics since the beginning of the 20th century, but in journalistic literature it continues to be widely used to refer to the American "mission" to promote democracy throughout the world. Understood in this sense, the “explicit purpose” of American statehood continued to influence the ideology of the ruling circles of the United States in the 20th century.

b) a state law could be declared illegal if it contradicted the constitution.

explanation:

the conflict of this case originated when james w. mcculloch, a cashier of the baltimore branch of the second bank of the united states that the congress had chartered in 1816, refused to pay a tax imposed by the maryland state.

in the case, the state of maryland appealed that the establishment of a second bank was unconstitutional since the constitution didn't say anything about granting that power to congress. however, the case determined that even if such right wasn't specifically stated in the constitution, it was part of the "implied powers" of the government enunciated in article i, section 8.

the case also eliminated maryland's legislation to impose taxes to a national bank, asserting that even though the states retained the power of taxation, the constitution's laws are supreme and can not be controlled by the states, therefore, if a state law contradicts the constitution, it should be declared illegal.

explanation:

it took two men to wrestle rome back from chaos and turn a republic into an empire. in the first century bc, rome was a republic. power lay in the hands of the senate, elected by roman citizens. but the senators were fighting for power between themselves.