What discouraged extensive european exploration of the continent and what invention allowed for the exploration later

When the united states entered world war ii it affect the lives of americans in many ways people were asked to such as food oil and gas the government awesome cars to purchase a to the country financially during the war more more working in all industries during the war

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What is the main difference between primary and secondary sources? a. primary sources are historical documents, and secondary sources are modern-day documents. b. primary sources are derived from museums and archives, and secondary sources are created by history students and academics. c. primary sources are found in ancient places with a rich history, and secondary sources are found in historical journals and blogs. d. primary sources are created during a particular historical era, and secondary sources are created by studying primary sources.