The became engines because when ever the Europeans crossed ocean they wanted more land and started pushing native turfs and destroying the recourses but also not all hated Europeans
I believe the answer is 4. During the reign of Askia Muhammad, the Songhai empire reached its greatest size.
Askia Muhammad was an emperor, military commander, and political reformer of the Songhai Empire in the 15th century. His rule resulted in trade with Europe and Asia, building of lots of schools, and spread of Islam through his empire.
Hope this helps! Please let me know if I'm wrong :)
Answer: The Suez Canal.
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Hope that helps! Best wishes.