Who were the israelites fighting in the time of Samuel when they lost 30000 soldiers?

During the time of Samuel, the Israelites were fighting the Philistines when they suffered a significant defeat, losing about 30,000 soldiers. This battle is described in 1 Samuel 4, where the Israelites initially brought the Ark of the Covenant into battle, believing it would grant them victory. However, the Philistines defeated them decisively, leading to a major setback for the Israelites.