Question

What was one significant development in the 20th century?​

Answer 1

Answer:

Notable developments included chemical warfare, the introduction of military aviation and the widespread use of submarines. The introduction of nuclear warfare in the mid-20th century marked the definite transition to modern warfare. Civil wars occurred in many nations.

Explanation:

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Answer 2

Answer:

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The century had the first global-scale total wars between world powers across continents and oceans in World War I and World War II. ... The 20th century may have seen more technological and scientific progress than all the other centuries combined since the dawn of civilization.