What is the difference between how scientists and historians use time periods?

Ahistorian who compares the expansion of political systems to the expansion of economic systems is organizing history by o a. region b. culture c. period d. theme

What event started the space race and made americans feel their security was threatened a.) alan shepard's suborbital flight. b.) the launch of sputnik c.) the launch of explorer d.) the cuban missle crisis

Need ! how did sumner define liberty in the book of "voices of freedom"