It is defined by the use of the word "citizen" throughout, as well as more generalized phrases such as "the people of the united states", etc.
"....or the right of the people peaceably to assemble...."
"...the right of the people to keep and bear Arms..."
"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated...."
"The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people."
All encompassing amendments such as slavery are more direct, "Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction."
It wasn't until the 11th or so that citizen replaced "the people" from that point on.
"All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws."