One of the most significant challenges is building an airplane had to do with "propulsion", since the technology that allowed motors to have enough energy to lift an airplane into the sky with a passenger wasn't available for most of history.
Continents were in different locations in the past and thus have moved (drifted) to their present location.
Wegener - Published controversal book on this theory in 1915.
Political authority grants members of a government the right to rule over citizens using coercion if necessary (i.e., political legitimacy), while imposing an obligation for the citizens to obey government orders (i.e., political obligation).
Hoped that helped:)
Okay so
14. I would say the answer to this one is: A new wave of nationalism.
15. The answer to this one is: Expansion of Slavery.
16. I think it is: The Taiping Rebellion.
I hope this helps you.