According to Jefferson, how do governments obtain their right to govern?

According to Jefferson, governments "derived their power from the consent of the governed."  This quote is from the Declaration of Independence.  In the document, Jefferson states that the people should be in charge of the government.  Most Western governments of that time period relied on either a ruling class or an autocrat, so this was quite a revolutionary statement.  Jefferson even gave the people permission to overthrow a government that did not rule with them in mind, but he advised the people to not enter into revolution lightly.  
Jefferson's statement that the people should rule has been used by people all over the world in their search for self-governance.  When Jefferson wrote this, he did not intend for it to include African Americans, women, Native Americans or poor people.  Since Jefferson's time, the definition of "the people" has changed to mean anyone over the age of eighteen, which is the voting age in the United States.  With more people to provide consent to the government, government has the potential to be more responsive to the needs of all.