Evolution of the Roman military system in the 1st-3rd centuries (from Augustus to Diocletian)

Education in August of the Institute of Permanent Army was a turning point in all further Roman history. Very soon became obvious that the safety of the empire requires more numerous armed forces. The main obstacles to the creation of new legions were financial difficulties. The high salary of the legionnaires and the inability to provide veterans in full reest assumed the government put the government before a practically intractable dilemma: how to reduce the cost of the maintenance of troops without prejudice to the state"s defense capability. Nevertheless, while the neighbors of the Romans in the West were crushed and forever begun with each other, the tribe of the Germans, and in the east - Parfyan, the collisions with which they were episodic, the military system, which was established during August, operated in general, well.
An unfavorable foreign policy setting led to the growing crisis phenomena in the entire Roman military organization. The crisis, who shook the Roman World in the III century, had a purely military character and was caused by the inability of the Roman military machine to function effectively in the changed political conditions. How successful were military reforms conducted by various emperors throughout the III century.? Was it possible to strengthen the military power of Rome during this period, or were all the expended efforts and enormous sacrifices were in vain and only for a while delayed the inevitable drop in the empire?