Slavery was a tragic but crucial element in the success of imperialism because slave labor was used in many European colonies to farm, build, and serve the colonists.

The correct option is : 
The Event that happened before U.S. Constitution was adopted : -
Harvard College was founded
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Kangawaya. I’m not really sure how to spell it out it basically said that China had to hand over Hong Kong and open up its trading ports and allow the sale of opium.