Question

How was the growth of the republic aided by the Roman army's use of legions on welfare

Answer 1

One of the reason why the Republic grew through their use of the Roman Army because they were composed of professional soldiers who were well-discipline and well-trained using tactics that exploited the weakness of their enemies. With every victory that they have in their campaigns, they also extended the rule of Rome in those areas.  This strengthen the Roman Republic.  Also the army was loyal and patriotic so it was natural for them to fight with commitment because they fight for glory of Rome.