nationis: nation, race, people, breed; pagan people
At least if you can trust the translator at this site: http://www.sunsite.ubc.ca/LatinDictionary/
Americanis - made it up. Guess I need to work on my Latin
nationis is the genitive form meaning “of the nation.”
natio is the nominative form — “the nation.”
Latin nouns take case endings. We don’t have them in English except with the pronouns — “he/him/his”, “we/us/our/ours,” etc.
The sunsite isn’t wrong — but you have to know what you’re looking at. Look up “natio” on that site — you’ll see the same translation.