What invention or innovation to make cities, factories, and railroads spring up in the north? iron steam engine cheaper steel better public education

Which statement best describes a significant cause of world war ii? o a. the economic boom that followed world war i allowed countries to build up huge militaries. o b. the treaty of versailles, which ended world war i, left lasting resentments in many countries. o c. the rise of imperial states in asia caused european powers to unite for their common defense. o d. the league of nations encouraged european states to form secret military alliances.