Originated in the 18th century when english impearialists were refering to their american possessions, most of which were in what would later become the USA.
Then the 13 colonies got independence, british possessions were limited to the Hudson Bay Company and Atlantic provinces of Canada (Newfoundland and what had been Acadia under the French) as well as a few islands in the West Indies. Since then Ameriker has been the way the English refer to the first land to break away from the British Empire.
Ameriker the Beautiful
Mall of Ameriker
you get ther point