As a slaveowner, Jefferson exposed himself to a charge of supreme hypocrisy for all eternity when he proclaimed that it was self-evident that all men were created equal. At first glance, equality does not appear to be essential to his overall argument for American independence. Why did he say it?
At the time, Americans were second class subjects of the British crown; after all, what was the point for the mother country in having colonies if you couldn’t exploit them? I think the equality argument was primarily intended to address that issue. In a sense, that is what the Revolution was all about; if you accepted the notion that there was such a thing as an “American” (given the ethnic and religious composition of the colonial population relative to the mother country and the very different nature of the land, there was), he was surely entitled to the same rights of self-determination as anyone in Great Britain.
In other words, it was an argument against imperialism. Happy Independence Day!