With the Israelites having been under Philistine control (see Judges 15:11; 1 Samuel 10:5; 1 Samuel 13:3, 1 Samuel 13:19), there would have probably been restrictions on any clan and tribal meeting. When the Philistines heard about a new gathering at Mizpah, they were concerned that it could be the beginning of another revolt against them.1 As a result, they dispatched a suitably sized military detail to enforce their regulations and protect their interests.
7 Now when the Philistines heard that the people of Israel had gathered at Mizpah, the lords of the Philistines went up against Israel. And when the people of Israel heard of it, they were afraid of the Philistines.