What prompted the Roman patricians to compromise with the plebeians when the plebeians seceded from Rome?

The one that prompted the Roman patricians to compromise with the plebeians when the plebeians seceded from Rome was: They realized that without the plebeians there would be no soldiers to protect Rome.

In Roman society, Plebian refers to the people from the lower social class (commonner). In their glory days, they rely on the power of the plebeians to defend their territory against Barbarian that tried to stole their crops.