The border of the children of Ephraim according to their families was [thus]: the border of their inheritance eastward was Ataroth Addar, to Beth Horon the upper;
Notice that Ephraim's territory was expanded by the assignment of some of the cities that belonged to Manasseh.  Cook stated that, "The reason for this can only be conjectured."[13]  With all that we learn of Ephraim from the prophecy of Hosea, we do not hesitate to assign as the reason for this enlargement the arrogance and ambition of Ephraim and that domination which he finally exercised over the whole ten northern tribes.  Ephraim, even before that enlargement, "had the rich district north and south of Shechem ... and the whole fertile plain of the Esdraelon."[14]  Also, we learn from  Joshua 17:14 that their unwillingness to clear out the Canaanites caused their complaint.  "Joshua, in effect, told them that if they were the great people they claimed to be, they could extend their territory by clearance and conquest."[15]