“Israel chose.” The text is literally “He chose,” but often “Israel” is used as a collective singular, and would take the pronoun “he.” It is also possible that “God” (Elohim) is the subject of the sentence and then it would read, “God chose new, then war was in the gates,” and “new” would be an adjective describing “new” leaders, such as Deborah, who then went to war (cp. NET). However, the fact that God consistently warned Israel that idolatry would lead to war and enslavement, and that is a major theme of Judges, is support for the traditional translation: “Israel chose new gods; then there was war in the gates” (cp. Deut. 32:17, “new gods”).
“Was there a shield or spear was seen among 40,000 in Israel?” The Canaanites had oppressed Israel for 20 years, and they disarmed Israel. This is still a tactic of the enemy today. A disarmed people is a weak and controllable people.