Mainframe computing was established by the late 50s, and mini-computing was just starting up. The market was already worth $billions by then. There were some prestige military projects - e.g. SAGE again - and a lot of DARPA funding for research. But the civilian market was already huge, with its own momentum.

Once TI introduced TTL logic in the early 60s, computers became a lot cheaper. At the same time a strong hobbyist culture fanned by magazines kept interest in technology running very high, so there was a steady stream of wannabe engineers with experience of digital techniques from their early teens.

Microprocessors were already being planned in the mid-60s. The biggest gap was between commercial computing and the microprocessor market, and that was bridged by developing a general purpose microprocessor and putting it into a commercial product - a dekstop calculator. It wasn't a military project.

Now you had hobbyist/hacker culture with access to microprocessors and a background of DARPA funded interface and networking research.

The rest was probably inevitable.

What's astonishing is how fast it happened. Most of the core ideas - laptops, databases, the web, GUIs and interactivity, distributed processing, networking, 3D graphics - appeared between 1958 and 1968.

There's been very little genuinely new since then. Most of what's happened has been faster and cheaper, but not so truly innovative.