What is the meaning of the phrase "contended even unto death for seven long years?"

“We hold these truths to be self-evident, that all men are created equal, that they are endowed by their creator with certain inalienable rights, that among these are life, liberty, and the pursuit of happiness ...”

This is the most famous passage of the Declaration of Independence, written in 1776 to justify a rebellion against the British Crown; that rebellion (“contention unto death”) resulted in the Treaty of Paris seven years later.