Why did internal change allow the Romans to win external victories?

Before you put things in order in the world, put it in your own home. This wisdom was confirmed by the Romans, having carried out a series of reforms in their state. The plebeians ceased to be a powerless part of society, from now on they could sit in the national assembly, pass laws, hold high positions and even marry representatives of the aristocracy. Such a social leap significantly strengthened the empire from within, giving it the opportunity to effectively pursue a policy of conquest, subjugating neighboring tribes.