That's in fact the story behind the end of the Republic. The old army was composed of owning class citizens who had no interesst in prolonging their military service by fighting private wars for their commander, nor was they anything the commander could offer them in reward, like land, what their did not already posses and run in danger of losing it when staying longer with the army.
The new armies were composed of men who were very much interessted to serve as long as possible, because they had no other business to return to. They were willing to follow their commander in every military adventure he might think of, as long as he gave them employment and the promise of a reward in the form of land afterwards.
The failure of the Senate was that it allowed powerfull citizens to raise private armies (for which in the end the state had to pay for) but failed to raise a regular standing army of this type loyal only to the Senate and the legaly elected magistrates. Of course, the condotteri of the Roman Republic were also important members of the Senate and (usually) legaly elected magistrates, what made matters even more complicated.
Augustus solved the problem by making himself the only owner of Legions, but that was only temporary. Later rebellious characters had no problems in using the professional army against their government and against each other. So this issue did not only cause the downfall of the Republic, it was also responsible for many severe crisis of the Empire and did a good deal to the downfall of that too.
What is said of the poor government of the Republic in her provinces is true in general - but does apply to more or less all larger states in pre-industrial times (and even to some modern too).
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