It is obvious that millions of Green Card holders are already eligible to apply for U.S. Citizenship. But why become a U.S. Citizen? Citizens are entitled to more rights. For one thing, Lawful Permanent Residents do not have the right to vote, nor can they run for elected federal and state offices. And while U.S. Citizens can sponsor a wide range of family members to the United States, permanent residents are allowed to sponsor certain family members and are often accompanied by lengthy approval times. In addition, permanent residents can never hold a federal job.
The graphic below shows the number of Green Card holders in the United States and their country of origin, as well as providing a schematic diagram that details the specific eligibility requirements before filing Form N-400, Application for Naturalization.