As an ill-informed IT person I thought the cable length for Ethernet was determined by timing, not signal strength.
That is somewhat true for the 10Base-2 (and the old 10mm yellow banana cable as well) network where you have a multidrop network made from coax and T-pieces.
For the other physical modes where you as discussed upthread have switches or run back-to-back between computers, distance is limited by attenuation. Electrical 10/100/1000Mbit Ethernet is -- by standard -- limited to 5+5+90 metres of cable (think switch -> patch cord -> patch panel -> fixed installed cable -> outlet -> patch cord -> computer) but in practice, and with fewer splices, can be run up to about 200 metres on good cable.
Optical has no practical limit, but you usually need an amplifier after ~110km of single mode cable, providing you have high-power transceivers. (People suggesting multimode should be taken outside and reeducated, mostly because multimode is an echo chamber where signals exit the Hall Radius after 550 metres at 1000Mbit/s. This is bad for you, and today is as expensive as singlemode.)
I have gotten 1000Mbit/s to work on 125 km, without intermediate amplifiers, using a long-range transceiver. We run a couple of un-amplified ~30 km links at 100Gbit (using 100G-BASE-LR4 which is a 4-channel DWDM around 1310nm) across town, and I'm just now preparing for a job where we'll be renting 100Gbit links over 600km spans. Those are handed off to us using 100G-BASE-LR4 as well.
Society evolution through technology tip: If you want your country to flourish, make sure that dark fibre is available and
cheap. It is an amazing force multiplier.