Brexit is a very deep and complex thing. Although at the highest, simplest level I imagine that if the American continent was federated and all those countries had free and open migratory access and citizens rights (including welfare) within each others countries, with the whole thing ruled and governed from a non-elected government in Columbia... that the majority of USA citizens would be anti the arrangement whilst the Mexicans, Nicaraguans, Costa Rican's et al would be very pro the arrangement. Especially so if a huge chunk of the USA tax dollar goes to those other countries for their advancement?
Of course the sanctimonious global-liberal would in a act of outraged indignation, would automatically condemn the USAEXIT voters as callous Nazi, Sexist, Racisits; as is within their mantra, the only perceived alternate to a fellow Liberal.
Of course as history shows time and again, all the federations and annexations of long established counties into newly formed empires or blocs always ends in a breakdown with every country seeking to regain its sovereignty, identity, nationality, Independence and autonomy. We hate our governments... until we lose them. Then we want self-government back.
Why should we ever learn from history?