Aliens are people who have left (emigrated) a foreign country to the United States. They have some of the same freedoms and legal rights as U.S. citizens, but they cannot vote in elections.
А уж что до слова "неграждане", то его вообще используют все кому не лень:
Chronology for Muslim (Noncitizens) in France
Residence information for non-citizenws, California
Over 112,000 residents of Japanese ancestry were subject to this mass exclusion program. Of those, approximately two-thirds were U.S. citizens by birth. The remaining one-third were non-citizens who were legally subject to internment under the Alien Enemies Act.