Actually, ‘1’ is the country code for the USA & Canada. The dialed preface ‘1’ instructs the end office switch (the one serving your house) to open a path to the toll switch (back in the days when LD calls were metered (charged by the minute.) which then routes the call inside the US & Canada.
If you dialed a ‘0’ first, the switch then knew it was an international call. In older times, it immediately prompted an international operator to pick up. Now it is all direct dialed.
The above information applied prior to the days of Number Portability which was mandated in the late 90’s.
As for the Exchanges (Klondike, et al.), these were the end offices in the neighborhood you live in. When I was a child we lived in the Lockheed section of Oakland. All phone numbers began with LO(X)-XXXX. When switch routing tables evolved, the geographical exchanges were dropped and they all went numerical.
>>Actually, ‘1’ is the country code for the USA & Canada. <<
Sorry I wasn’t clear — the “1” in the exchange preceded country codes.
That is why we de-facto settled on “1” for USA and Canada — most phones in the world were in those countries and the switching hardware were already wired to react to “1”