When Jacob, called Israel, was nearing death, his son Joseph brought his own two sons, Manasseh and Ephraim, to be blessed by Grandpa Jacob. In contrast to the proper way things are done, Jacob placed his right hand on Ephraim (the younger) and his left on Manasseh (the older). Joseph went so far as to try and correct his father, thinking Jacob’s eyesight was to blame. But Jacob insisted, and stated that Ephraim would be the greater and his descendants would be “a group of nations” – a way of saying “lots and lots of people!”
Ephraim was just a kid when Jacob gave this blessing. Five hundred years later, when Moses wrote down this account, the tribe of Manasseh outnumbered the tribe of Ephraim by a significant number (about 20,000 more men than Ephraim). By all logic, it seemed like Jacob’s blessing had been mistaken, and you can well imagine Moses scratching his head, thinking, “But Manasseh is way bigger than Ephraim…”
But by the time of the Judges, generations after Moses had died, Ephraim became larger than Manasseh. By the time the kingdom of Israel divided, Ephraim had become the second largest tribe, with only Judah the larger.