What lead to American imperialism

Nationalism led to major conflicts following world war i, especially when:

During the growth of colonial america, people saw the need for a colony between south carolina and the spanish in florida. james oglethorpe and 19 settlers were told to start the colony of georgia. which coastal city did oglethorpe and his settlers found? a. jamestown, virginia b. savannah, georgia c. st. augustine, florida d. atlanta, georgia

What change took place in the african slave trade in the 1500's?