X= least important cause or consequence with explanation why

A,B, C = least important cause or consequence, with explanation why
Y= your assertion statement

can someone plz explain what the thesis formula means and how to use it

my topic is Analyze the Impact of the Atlantic System on the development of the British North American colonies during the 17th and 18th centuries

This part makes no sense to me, if X is also supposed to be the least important cause...

A,B, C = least important cause or consequence, with explanation why