What does this essay prompt for The Outsiders mean? "An individual identity of a person is determined by their external influences. Discuss this...

This essay prompt wants you to address how events in the book influenced Ponyboy.

Ponyboy’s life is greatly influenced by external forces.  This just means factors outside of himself that he cannot control.  In writing your essay, these are the points you will want to include.

One of the biggest external factors is that he is a greaser, in a town where the greasers and Socs are always at odds.  This influences most of his life and all of the events in the book.

Greasers can't walk alone too much or they'll get jumped, or someone will come by and scream "Greaser!" at them, which doesn't make you feel too hot, if you know what I mean. We get jumped by the Socs. (Ch. 1) 

Pony is proud of the fact that he is a greaser, but it is a source of shame and worry too.  He worries that the Socs will jump him, but he is also aware that everyone is judging him.  He likes being a greaser because it gives him a sense of belonging, but he doesn’t like the fighting. 

The biggest external event is when Johnny and Pony get attacked by Bob and Randy.  This fight is a result of Johnny and Pony making friends with the Socs’ girlfriends, Cherry and Marcia, while at the movies.  The Socs find them later in the park, where Pony ran away from Darry when he hit him for coming home late. 

Randy, Bob, and three other Socs find Johnny and Pony in the park and begin hassling them.  Johnny is frightened, because these Socs have jumped him before.  He pulls out a switchblade, but Pony has no weapon.  When Bob is drowning Pony in the fountain, Johnny intervenes. 

Bob, the handsome Soc, was lying there in the moonlight, doubled up and still. A dark pool was growing from him, spreading slowly over the blue white cement. I looked at Johnny's hand. He was clutching his switchblade, and it was dark to the hilt. My stomach gave a violent jump and my blood turned icy. (Ch. 4) 

Pony is a good person, and so is Johnny. They were trapped by circumstances.  Because the Socs relentlessly targeted them, Johnny felt like he was in deadly peril.  Johnny and Pony had to go on the run because they did not think the police would believe a couple of greasers.

You can see how external influences can affect a person.  Pony and Johnny were not violent by nature.  The fact that they were greasers, and they met two Soc girls, resulted in Johnny killing Bob and the two of them running away.  This of course also directly led to the events of the church fire, where Pony was hurt and Johnny later died as a result of his injuries.