You didn’t put choices for what we can pick from, but as far as i can see, i would put Aztec Religion!
Explaining: If they feared the Aztec people then i would assume that they also fear their religious practice!
Apparently, all of the names on the map are Irish, so the map suggests that Irish immigrants may take over the United States by the 1900s.
You may well be right about people's fears that immigrants, lots of them from Ireland, would overrun the country. Look up when the potato famine was, though. The map may be from the early 1900s, but, if so, not about the potato famine in Ireland.
You need to be more specific please
