I'm gonna go with C) The idea that all people are entitled to political equality. but please let me know if I'm wrong.
Im assuming that you are asking about the Constitution. Article 2 section 4 of the Constitution literally says, “The President, Vice President and all civil officers of the United States, shall be removed from office on impeachment for, and conviction of, treason, bribery, or other high crimes and misdemeanors.”
Better jobs & opportunities.
A push factor would be like famine or disease in the country, etc.