In 1915, Freud had suggested that the frustration of behavior aimed at gaining pleasure or avoiding pain led to aggression. In 1939, this hypothesis was further developed by Dollard, Doob, Miller, Mowrer & Sears, who were interested in integrating the concepts arising from learning theory and psychoanalysis. They proposed that 'the occurrence of aggressive behavior always presupposes the existence of frustration and, contrariwise, ...the existence of frustration always leads to some form of aggression'.

Simply stating, aggression is a response to the frustration of some goal-directed behavior by an outside source. Goals may include such basic needs as food, water, sleep, sex, love, and recognition.



Evidence exists that when frustrated, individuals do not always respond with aggression. They show many different reactions, ranging from sadness, despair, and depression on the one hand, to direct attempts to overcome the source of their frustration on the other. In short, aggression is definitely not an automatic response to frustration.

Second, not all aggression stems from frustration. Frustration is simply one of many factors that can potentially lead to aggression. However, frustration can serve as a powerful determinant of aggression under certain conditions— especially when it is viewed as illegitimate or unjustified (e.g., Folger & Baron, 1996).

In 1908, Alfred Adler proposed that aggression was an innate, primary instinctual drive. All behavior stemmed from an aggressive 'masculine protest' against feelings of inferiority, sexuality being reduced to the man's aggressive attempt to master the woman.

In 'Instincts and Their Vicissitudes' (1915), Freud suggested that aggressiveness, too, was a component of the ego instincts - aggression, in other words, was at last given a formal place in the theoretical scheme, though not yet as a full-fledged, separate instinctual drive in its own right (Nemiah, 1966).

In 1920, with a drastic revision of his theory, Freud subsumed both sexual and self-preservative instincts under Eros - the life instinct - and postulated the existence of the death instinct, in opposition to Eros. Aggression was now no longer considered to have its origins in the self-preservative instincts, but in the death instinct, and Freud compared the polarity of love (affection) and hate (aggressiveness) with the polarity of the life and death instincts. Death instinct is initially aimed at self-destruction, but is soon redirected outward, toward others.

Aggression springs mainly from an inherited fighting instinct, which ensures that only the strongest males will obtain mates and pass their genes on to the next generation (Lorenz, 1966, 1974)

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In 1908, Alfred Adler postulated the theory that aggression was an innate, instinctual drive. In 1915, Freud suggested that frustration of behavior aimed at gaining pleasure or avoiding pain led to aggression. Later in 1920 he related aggression to Thanatos, the death instinct. These form the core of the psychodynamic theory of aggression. In 1939, Dollard, Doob, Miller, Mowrer & Sears, further proposed that aggression is caused by frustration and frustration causes aggression, thus forming the Frustration-Aggression hypothesis.

Sources:
http://rint.rechten.rug.nl/rth/dennen/a-panal.htm
Gale Encyclopedia of Psychology
Social Psychology, 12th Edition by Robert A. Baron, Nyla R. Branscombe, Donn R. Byrne, Gopa Bhardwaj (Click for eBook)