The Resistance was the exact same thing as the Rebel Alliance in every way, but it was much older. After the Rebel Alliance successfully defeated the empire they never managed to take the galaxy back and make things better by creating a stable New Republic. The reason they changed their name was so they looked like they actually changed something. They actually had less ships than the rebel alliance did, they completely lost their A-wing Y-wing and B-wing fighters, but they had a few old X-wing's. Therefore they had to do bombing runs with X-wing's, which they were not made for.