Wars of necessity are essentially unavoidable. They involve the most important national interests, a lack of promising alternatives to the use of force, and a certain and considerable price to be paid if the status quo is allowed to stand. Examples include World War II and the Korean War.
You prevent kids from joining gangs by offering after-school programs, sports, mentoring, and positive engagement with adults. You intervene with gang members by offering alternatives and employment to help redirect their lives. You deal with areas of high gang crime activity with real community policing. We know what works.