Bureau of Sabotage
Rebel Insurgency: Without Hope or Method
The Rebel Alliance is going to lose, not because they are outnumbered, but because they have no model on which to base plans for their campaign. There are essentially two kinds of insurgent campaigns: city-out or countryside-in; Leningrad, or Yorktown. The Rebel Alliance is fighting both of them wrongly, and has few chances left before defeat and dissolution.
The First Order, for its part, is not a foreign force; they are fighting a campaign of imperial consolidation (think: the Union side in the US Civil War, or the British side in the Boer Wars or the War of Continental Independence) not a conquest from outside. As such, they fail to seize most of the advantages of supply and maneuver their better trained, better equipped, larger force offers.