Why didn’t god do this before?

Numbers 22:11 says, “Behold, there is a people come out of Egypt, which covereth the face of the earth: come now, curse me them; peradventure I shall be able to overcome them, and drive them out.

22:12 And God said unto Balaam, Thou shalt not go with them; thou shalt not curse the people: for they are blessed.

22:13 And Balaam rose up in the morning, and said unto the princes of Balak, Get you into your land: for the LORD refuseth to give me leave to go with you.”  Why didn’t god do this with the Amorites in Numbers 21?  He could have saved countless lives of men, women, and children.