Why was Balak, king of Moab, afraid of Israel?
Balak was afraid because Israel had utterly destroyed the Amorite tribes, and word of their victories spread by camel caravans and gossip until Moab heard. The Moabites had heard all that happened to the children of Israel. Verse 3 says he was sore afraid because the people were many.
Les explains that Balak, the son of Zippor, king of Moab, had seen and heard all that Israel had done to the Amorites. Israel had already fought battles and utterly destroyed Amorite tribes, so news spread by word of mouth. As camel caravans traveled from Egypt up into Mesopotamia, people gossiped and told everything they knew, so by the time Israel reached Moab, the Moabites had heard all that had happened to the children of Israel, even back to their exodus. In verse 3, Balak was sore afraid of the people because they were many.
And Moab was sore afraid of the people, because they were many: and Moab was distressed because of the children of Israel.