Due to the columbian exchange different plant's animals and diseases were carried across the Atlantic. Potatoes, peanuts, corn and cocoa arrived in Europe from the Americas. Horses, pigs and goats were brought from Europe to the Americas. The European travelers also carried diseases, such as smallpox, that the Native American population wasn't immune too.
In time a fifth group was added to the cast system-- the untouchables is the correct answer.
It involves problem identification
Answer: The Aftermath of World War I saw drastic political, cultural, economic, and social change across Eurasia, Africa, and even in areas outside those that were directly involved. Four empires collapsed due to the war, old countries were abolished, new ones were formed, boundaries were redrawn, international organizations were established, and many new and old ideologies took a firm hold in people's minds. World War I also had the effect of bringing political transformation to most of the principal parties involved in the conflict, transforming them into electoral democracies by bringing near-universal suffrage for the first time in history, as in Germany (1919 German federal election), Great Britain (1918 United Kingdom general election), and Turkey (1923 Turkish general election).
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