<span>an expert in or student of history, especially that of a particular period, geographical region, or social phenomenon.</span>
After WWI and during the Great Depression the US tried to be an Isolationist nation. They put out tariffs so people would buy US (forgetting that the rest of the world was still devastated by WWI (economies included)).
Social Darwinism<span> was a sociological theory popular in late nineteenth century europe and the United States. Maybe?</span>
About 35 years. Genghis Khan created the Mongol empire in 1206. By the 1230s Batu Khan invaded Russian and Bulgarian lands. In 1241 at the battle of Mohi Batu Khan defeater a combined German, Polish and Hungarian army. Further expansion ceased do to the death of Ogedei Khan. Batu Khans attention was turned to succession instead of invading Western Europe.
