Genesis 48:18

Not so, my father. Assuring Joseph that Manasseh, the elder of the two, would also become a great nation, Jacob stated emphatically, however, that Ephraim would become even greater, a “multitude of nations,” or, more literally, a “fullness of nations.” This blessing began to meet its fulfillment from the time of the judges onward, by which time the tribe of Ephraim had so increased in extent and power that it took the leadership among the northern ten tribes, and its name acquired equal importance with the name Israel (see Isa. 7:2; Hosea 4:17; 13:1; etc.). At the time of Moses, Manasseh numbered 20,000 more than Ephraim (Num. 26:34, 37). Subsequent history shows that this promise was from God, and that the blessing of Jacob was not merely the pious wish of a dying grandfather but the actual bestowal of a blessing of definite prophetic significance and force.