I am a firm believer that the legacy carriers don't really have "fare wars" any longer like they did 30 years ago. Most things are controlled by capacity. They can (for instance) file a $200.00 fare MSP/RSW RT but just not have inventory. Then if the flights prove to not be selling, they open up lower fare inventory on specific flights or dates. That is also why you might see variance in fares from day to day as inventory comes and goes. Also prevents mass discounting in markets where they don't need it. Everybody has their own theory. Only their hairdresser and revenue management know for sure.