His main contribution was the powerful , widely-read pamphlet Common Sense ( 1776 ) , advocating colonial America 's independence from the Kingdom of Great Britain , and of The American Crisis ( 1776 â `` 1783 ) , a pro-revolutionary pamphlet series . His principal contributions were the powerful , widely read pamphlet Common Sense ( 1776 ) , advocating colonial America 's independence from the Kingdom of Great Britain , and The American Crisis ( 1776 â `` 1783 ) , a pro-revolutionary pamphlet series .