Wiktionary
break the back of
vb. (context idiomatic English) To achieve the greater part of some project.
Usage examples of "break the back of".
One way or another, I will have to break the back of their alliance in Sulla’.
Old disputes had been forgotten and in the end they had all sent their best men to aid the High King and break the back of the Roman occupation.
One way or another, I will have to break the back of their alliance in Sulla's name.
No longer will your sons go up to the altar of Huitzilopochtli, for I will break the back of the Mexica, I will tear out the heart of the Tlaxcala, and your ships will touch the shores of all the islands of the world.
When spring arrives, we will take Aydindril and break the back of the New World.