In this chapter, Israel turns back to idolatry and the LORD gives them over to the Philistines and Ammonites.
The story here should be getting very familiar. It starts off with two heroes who "save Israel" from various troubles, and again both of them are from northern Israel (one is from Issachar, the other from Gilead in Manasseh). This whole book seems to be biased towards northern Israel and especially Gilead. We can suspect that the author might be from northern Israel or Manasseh.
After these two heroes die, Israel returns to idolatry, serving the gods of all the nations around Israel and from within the land, which is again very familiar.
Before the LORD sent Gideon to save the people, he also sent an unnamed prophet to rebuke the people for their idolatry. This time the LORD rebukes them again, telling them to ask their new gods for help if those are the gods they wish to serve. This chapter doesn't tell us how the LORD shared this message, but it was most likely through a prophet or something similar.
Most of the enemies listed here are nations that attacked Israel earlier in Judges, such as the Amalekites, Ammonites and Philistines. The LORD also mentions the Egyptians, who haven't fought against Israel since they departed during the exodus. The LORD further mentions the Sidonians and Maonites (the people from Maon, a town in Judah, Joshua 15:55), which we haven't heard had been oppressing Israel. It's possible they were lesser allies of earlier oppressors. Who knows, it's not really that significant.
The main purpose of this chapter is to set us up for the next chapter, when the next hero of Israel emerges to save them from their enemies on behalf of the LORD. Having "put away the foreign gods from among them", it seems inevitable at this point that the LORD will indeed save them. I can only ask for how long it will remain thus, before Israel returns to sin. Honestly I would say more but this is a pattern we have seen multiple times now and it's really the same thing all over again.