Another blog that I would like to recommend is John Robb's excellent Global Guerrillas, which tracks the changes in strategy that are being adopted by non-state combatants around the globe. Two recent entries, When will Brazil's Gangs Make the Jump? and A failure to embrace black globalization in Somalia, are good examples of his thesis.
I'm no expert in modern warfare, thank god, but his thoughts on the nature of 21st century war seem to be on the mark. I wish his posts were longer, and I have a vague discomfort over his use of the term 'open source' to describe the warfare of guerrilla groups, but those are minor quibbles.