Theirs the 3 oaths- which actually weren't and aren't Halacha (binding as law, for the majority of poskim) , but even if it was , it was breached by the nations. In brief
- ( Ketuvot 111a ) - Im quoting from Rabbi Kahane's book Ore Harayon chapter 26 (the whole chapter is on this).
" What are the 3 oaths? G-d made Israel swear not to go up to the Land en masse; [Rashi: "together, by force"] and not to rebel against the nations, and He made the nations swear that they would not subjugate Israel too much. "