What topic is often used as a theme for studying world history since world war i?

The topic that is often used as a theme for studying world history since World War I is decolonization and nationalism.

Decolonization and nationalism were used because these are closely related themes to the causes and effects of World War I. Decolonization was an effect of the end of World War I, while nationalism is the factor which helped nations conquer the odds brought by the war.

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: