So if Leia didn't create the Resistance, the First Order wouldn't have destroyed the New Republic? That was their stated motivation after all.
General Hux: We shall destroy the government that supports the Resistance, the Republic. Without their friends to protect them, the Resistance will be vulnerable, and we will stop them before they reach Skywalker.
Seriously, the only thing that the First Order wants is to wipe out the Resistance. Hux's talk of systems bowing to the First Order could just be a means to motivate the First Order, not something they were literally going to do. If dominating the galaxy was their whole point, you'd think they'd bring that detail up in their closed doors meetings. But no. All they want to do is destroy the Resistance. For all we know, the First Order wanted to be left alone in a Jedi-free galaxy. And given the Jedi's history of 'not giving a crap' about anything and sometimes make things worse, that's not an unreasonable idea.