I over thought this a lot and the only conclusion I could come to is the earth nation should be covered in railway lines. Extremely shortly after some of the first viable self-propelled steam locomotives were invented the first railwaya were built, and within 50 years entire countries were covered in railway lines connecting the smallest towns both that existed before the railroads and many built by the railroads.

The existence of bending would only accelerate this development since right of way would be rapidly built through earth bending, and locomotives could simply have a closed system of water to be bent to produce propulsion. An earth bender could also spin a stone flywheel attached to gears to produce propulsion too. Or combine these with steam propulsion to overcome the limitations of early steam engines and the poorer iron and steel alloys of the time