The way formed Social Networking

When we talking about the birth of social networking, we need talking about origin the birth of social networking.

The second and third industrial revolution (late 19th century - early 21st century), associated with the electrification process (automatic machine and automatic machine system, robots, automatic control system). The pioneers are Nikola Tesla, Thomas Alva Edison, George Westinghouse and Frederick Winslow Taylor.
Successive the achievements of the Third Industrial Revolution, humans invented the computer:

ENIAC – Electronic Numerical Integrator And Computer (1945-1946) - The first digital computer was developed by Professor Mauchly and his Eckert student at the University of Pennsylvania.
Don Estridege - father of the IBM PC (1981) - precursor of PC today.
The birth of the computer paved the way for the birth of internet:
In 1969, the US Department of Defense built the ARPANET project to study the network.
In 1972, Bob Kahn showed the ARPANET network linking 40 pc through the communication processors between the Terminal Interface Processor-TIP (precursor to today's Internet).
And the explosion of internet in the late 21st century has led to the emergence of social network:
In 1994, Geocities was founded (the world's first social network).
In 2001, Friendster was formed.
In 2002, MySpace
In 2004, Facebook
In 2006, Twitter and etc...
What is the most important factor leading to the birth of social networking?