The words and sentence construction of all living languages are constantly changing, so who gets to make the rules of American English?

I think the British

Explanation:

The British colonization of the Americas is the history of the establishment of control, settlement, and decolonization of the continents of the Americas by England, Scotland and (after 1707) Great Britain. Colonization efforts began in the 16th century with failed attempts by England to establish permanent colonies in North America. The first permanent British colony was established in Jamestown, Virginia in 1607. Over the next several centuries more colonies were established in North America, Central America, South America, and the Caribbean. Though most British colonies in the Americas eventually gained independence, some colonies have opted to remain under Britain's jurisdiction as British Overseas Territories.