Security clearance is required in many job positions that have affiliation with the government. Because these jobs come in touch with the top secrets of the government, they want to make sure you won't go around telling the whole world. But in order to get a security clearance you must be a U.S. citizen or a U.S. person. If you have only a visa or permanent residency then it will not be valid. Having U.S. citizenship ddemonstrates that you have complete loyalty to the United States and no one else.
