Why is the 1920's considered the first decade of the modern era

During the cold war, which of the following groups of countries would have all been"behind the iron curtain"

What event led to the progressive movement?

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.