Interesting observation after the quick Google searches (so admittedly the data is not precise, but still should be in the ball park).

El Salvador's population is a little over 6 million, while NYC's population is a little over 8 million.

Murders in El Salvador average around 4,000/per year, while murders in NYC average around 500/per year. NYC's population is 25% greater than El Salvador's. The murder rate in El Salvador is 7 to 8 times greater than NYC. In and of its self I guess it doesn't mean much, but it does put in context. if NYC had the same rate, we would lose as many people in NYC to violence in one year as we lost in Iraq during all of OIF.

Easy to see how a how a government in a relatively poor nation was overcome with this level of violence and decided to negotiate. Is negotiating capitulation or a reasonable response in this case?