Socially ( this I'm only guessing at):  At the time of Rome's weakening, their was an increasingly widening gap between the plebian and patrician classes do to the poverty of the plebians and the extreme richness of the patricians.  This cause for social conflicts and a fall in the plebians morale who were, of course, the majority.  When the government saw this, they created a huge number of holidays ( somewhere in the upper 100's) throughout the year and made such places for public amusement such as the coliseum ( they also had huge mass orgies...but let's not go there!)  This created for a general loss of patriotism in the populace, and a loss of contact with the ruling class through the wide gap between the classes, and a lack of confidence in the now faltering Roman Empire. 

 

   Politically:  Rome, had become to great and vast for it's own good.  Their empire had swelled to proportions which it's government was unable to effectively control.  With the encroaching and increasingly brazen attacks of Germanic tribes from the west, Rome needed complete and swift control, and this it lacked.

 

  Militarily:  While Rome possessed a brilliant war machine, they, in a political attempt to strengthen control, halved their military abilities  with the division of Rome into east and west empires.  Also, the instability of the weakening Roman empire, and lack of great leaders, resulted in a loss of morale, or more accurately, fighting spirit.  Soldiers were no longer fighting for the glory of the empire, they were fighting for wages, and those were not much at all and certainly not to die for.

     Economically:  Another situation, like the political/geographic scenario, where Rome became perhaps, too good.  Rome's wealthy patricians spent exorbitant fees to foreign sources to decorate their homes, and buy their foods, and fund their parties.  As happens with many empires, their gold leaves the country through an imbalance of trade.  Rome was slowly draining of it's wealth