I think TFA should open with the Republic dominant, but divided. There are two major groups within it: those who support the First Order, and those who support the Resistance. That’s why they don’t just send the New Republic fleet to fight the First Order: it’s officially neutral. Think of it like Vietnam. It’s a proxy war, with two great powers fighting through smaller militia. Of course, TFA ends with the Senate destroyed (obviously I’d swap out the superlaser for a dreadnought, but the result is the same), so now it’s open war.