My personal picks would be the whole of Chinese history between the opium wars and communist rule (or the century of humiliation as it is called), and most especially the warlord era, given that this was effectively how European powers, Japan and many internal revolutionaries managed to bring down the greatest economy in the world to civil war and then total warlordism for 40 years. For a vague concept, my pick would be the great divergence, the period where the US and European nations rose above the rest of the world and became the predominant world powers and colonized most of it, along with the many potential causes of this.