The most accurate words to fill the spaces would be:
Sugar plantations were the backbone ( source ) of the economy.
In 1890, the US Congress passed the ( McKinley Tariff ), which removed tariffs on all foreign sugar imports.
Hope my answers have come to your help.
Desire of the railroad companies to build rail lines on a deal of new land that open up to whether it was for the "free" or "slaves" .
B. peacefully divide African territory between European empires.