What would happen if mexico tried to invade central america?

Mexico would lose and badly. True Mexico has more numbers and weapons, however they are clueless. they have no real training most of there combat tactics involve "Spray and Pray". South American countries no how to fight, even most citizens are trained due to local militias. There militias are everywhere, well trained and often supplied by there own governments just in case something like this happens. The same thing happened in WW2, Switzerland was right in the middle of the whole conflict, but they remained neutral to the whole war. No one dared invade them them because they don't have strict gun regulations like they do in the good old USA. Private citizens are allowed to own fully capable machine guns. It would never work for the invaders there would be a huge fire fight at every neighborhood.