Gideon's sons... and Abimelech
Gideon had many sons:
Now Gideon had seventy sons who were his direct descendants, for he had many wives. His concubine who was in Shechem also bore him a son, and he named him Abimelech. -Judges 8:30-31, NASB
Abimelech wasn't included in the same group as Gideon's seventy sons because he was born to his father's concubine (NCV "slave"), who lived in Shechem.
After the death of Gideon (a.k.a. Jerubbaal), Abimelech conspires to seize the kingdom from his father's seventy sons. He goes to the people of Shechem and appeals to them to follow him:
And Abimelech the son of Jerubbaal went to Shechem to his mother’s relatives, and spoke to them and to the whole clan of the household of his mother’s father, saying, “Speak, now, in the hearing of all the leaders of Shechem, ‘Which is better for you, that seventy men, all the sons of Jerubbaal, rule over you, or that one man rule over you?’ Also, remember that I am your bone and your flesh.” -Judges 9:1-2
Abimelech went to his mother's relatives (the people of Shechem)...
...to the whole clan of the household of his mother's father...
and urged them to follow him and not Gideon's seventy sons, because he was their bone and their flesh.
By this time, Shechem had been completely conquered by Israel and the city was presumably inhabited entirely by Israelites. (cf. Josh. 24:25) Here's what I don't understand:
If Shechem was an Israelite town full of Israelites, and his mother was one of the people of that town, part of that clan, a relative to that people, why would she, an Israelite, be a slave / concubine who was unfit to be considered one of Gideon's wives, and whose son was unfit to be numbered among his direct descendants?
If Abimelech's mother was not actually an Israelite, but some foreign slave / concubine, why would Abimelech specifically appeal to the Shechemites to follow him and not Gideon's seventy sons on the basis that he was their relative?
If the Shechemites were not Israelites, how is it that Joshua, at the end of his portion of the conquest of the Promised Land, mediated a covenant between God and the Israelites in Shechem?!