The phrase “the children of Israel did evil” (in some modern translations, “people”) appears exactly seven times throughout the book of Judges, once in the introductory summary and once at the beginning of each of six of its twelve historical sections. In order, these are: Othniel (oppressing nation: Mesopotamia, period of national servitude: 8 years); Ehud (Moab, 18 years); Deborah (Canaan, 20 years); Gideon (Midian, 7 years); Jephthah (Ammon, 18 years); and Samson (Philistines, 40 years).
So then, six notable periods of extended oppression from six different nations, totaling 111 of the 300-plus years the judges judged Israel.