Start in 1635 and travel from port to port and recruit as many marines as possible (100) whilst heading south-west go to cayman islands and attack select put all marines in last option area once on land take prisoners but not back to ship keep taking prisoners and decline terms the town will surrender you will get an option to sell prisoners click it then click cancel the money you are rewarded for defeating them will go up each time you offer to sell them and cancel

(the more houses you raid the more the multiplier
also raid the treasury but not governers mansion)
(having 100 muskets will speed up process rapidly)