In 1945, there were literally a total of a few hundred phone lines fully crossing the United States. A few bundles of twisted pair running across the Colorado mountains and New Mexico desert. If you wanted to make a phone call from New York to San Francisco, you booked ahead of time and paid out the nose for a noisy line. Such services were still revolutionary -- they had only become generally available c. 1920. And there was certainly no such thing as long-distance television.
Just 15 years later, you could place a direct-dial call between almost every major city in North America, it would probably connect instantly, and cost 1/20th the rates of two decades before. The entire nation would tune in to watch simulcast television on both coasts.
They connected the majority of urban areas with broadband pipes measuring tens of MHz of bandwidth available for TV and data, and thousands of voice channels. A continent-spanning network of coaxial and microwave relay towers - multiple redundant routes with hundreds and hundreds and hundreds of those Long Line installations -- all constructed in the span of about a decade to the cost of something like $60+ billion in modern money. It's one of the greatest crash infrastructure projects any society has ever undertaken.
The system in 1960: http://www.long-lines.net/places-routes/maps/MW6003.jpg
Once a significant opportunity presents itself, we really can move mountains.
Seems amazing now, but it was only 30 years before in 1915 when Graham Bell in NYC talked to Watson in San Francisco. That was thanks to the wire finally existing and tube amplification finally showing up. (So hard to find good, close-up details on that 30 years.) 1945 when Arthur C. Clarke proposed a 3-satellite system. 1963 when Relay 1 and geosynchronous Syncom 2 showed up.
'Microwave towers' ... for those who haven't seen them, this article goes into what's left of them - with pix. [https://99percentinvisible.org/article/vintage-skynet-atts-a...]
It was fairly agnostic to the actual contents of the channel as long as it fit within the assigned bandwidth. For example, they started using broadband digital modems to carry PCM audio by the 1970s, in parallel to the TV and FM voice. The circuit and packet-switched computer networks AT&T later provided were first carried this way too, as I understand it.
In practice, NBC/ABC/CBS were the biggest clients and used it to relay live network programming, etc. until satellites started displacing that in the 1970s. But it got used for all sorts of esoteric purposes too. Anything you needed bandwidth for, if you could afford it.
Why? Federal funds, and the Government finally interconnected itself.
Amazing, not really, corporation taking advantage of a new opportunity, Yes.