The dancing plague of 1518 was a three-month-long dance marathon where citizens of Strasbourg danced to the point of exhaustion and even death. Some theories pose the dancing plague was caused by hallucinogenic ergot, psychological stress, or a religious cult.

The fall of Rome, a far-reaching and dominant Roman empire, was caused by internal division, corruption, tax evasion, labor shortages, religion, and invasions from more powerful armies.

Chinese communist leader Mao Zedong called upon China’s youth to purge the “Four Olds” in a cultural revolution. The result would be widespread harassment, imprisonment, violence and anarchy.

After Joseph Stalin declared himself dictator in 1929, he began his Great Purge of former allies, Bolshevik enemies, or anyone perceived as a threat to Stalin’s power. Ultimately, the Great Purge extended into genocide of peasants, ethnic minorities and even children.

The modern history of Hong Kong is rooted in the Opium Wars, which resulted in Britain obtaining a 99-year lease on the territory, establishing a financial hub for decades before repatriating Hong Kong to the People’s Republic of China in 1997.

The Mesolithic period is nestled between the Paleolithic and Neolithic periods and saw the rise of agriculture and animal husbandry to replace the prevailing hunter-gatherer culture, which archeologists and historians believe was an unevenly-embraced advance.

German foreign secretary Arthur Zimmermann’s telegram to Mexico in 1917 was intercepted and deciphered, prompting the U.S. to rescind isolationism and declare war on Germany, officially entering WWI.