The Israelites had just crossed the Jordan River as their parents’ generation had crossed the Red Sea some 40 years earlier. Some of the older people there (who were children at the first crossing) would have done both.
News of this miracle got back to the kings on the western side of the river:
Joshua 5:1 When all the Amorite kings west of the Jordan and all the Canaanite kings who lived along the Mediterranean coast heard how the Lord had dried up the Jordan River so the people of Israel could cross, they lost heart and were paralyzed with fear because of them.
It’s likely that they were relying on the flooded river to give them some defence against the invading Israelites. Not only were those kings now confronting an army in their hinterland, but the army clearly had supernatural help again.
Everyone already knew what God had done for the Israelites, as Rahab explained:
Joshua 2:9-11 I know the Lord has given you this land. We are all afraid of you. Everyone in the land is living in terror. For we have heard how the Lord made a dry path for you through the Red Sea when you left Egypt. And we know what you did to Sihon and Og, the two Amorite kings east of the Jordan River, whose people you completely destroyed. No wonder our hearts have melted in fear! No one has the courage to fight after hearing such things. For the Lord your God is the supreme God of the heavens above and the earth below.
But then the Israelite men all got themselves circumcised and had to sit around until they healed. Why did the Canaanite and Amorite kings not know about it? Why didn’t they take what would have been the one chance they had and attack Israel? Were they too afraid to even spy on their enemy?
Instead, they watched as the men rested and the women harvested grain to make bread after the Passover:
Joshua 5:11-12 The very next day [after the Passover] they began to eat unleavened bread and roasted grain harvested from the land. No manna appeared on the day they first ate from the crops of the land, and it was never seen again. So from that time on the Israelites ate from the crops of Canaan.