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.

evaluate the extent to which the seven years' war (french and indian war, 1754–1763) marked a turning point in american relations with great britain, analyzing what changed and what stayed the same from the period before the war to the period after it.

b is the answer i am assuming