Short answers, pulled from the story.
Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation via high-voltage transmission lines. Distribution refers to the local wiring between substations and end customers, which operates at lower voltages; the two functions are distinct in the power industry, though they together form the electrical grid.
Transmitting at high voltage reduces current, and because energy losses are proportional to the square of the current (Joule's first law), higher voltage dramatically cuts losses. For example, a 100-mile span at 765 kV carrying 1,000 MW loses 0.5%-1.1% of power, while the same load on a 345 kV line loses 4.2%.
The first long-distance AC transmission line was 34 km long, built for the 1884 International Exhibition of Electricity in Turin, Italy. It was powered by a 2 kV, 130 Hz Siemens and Halske alternator and used several Gaulard transformers to feed incandescent lamps.
High-voltage direct current (HVDC) is used to transmit large amounts of power over very long distances or to connect electricity grids that are not synchronized with each other. It is also used in submarine power cables, where AC is impractical due to cable capacitance; the longest operational submarine HVDC link is Viking Link between the UK and Denmark at 765 km, as of the 29th of December 2023.
The US Northeast experienced major blackouts in 1965, 1977, and 2003. Major blackouts also struck other US regions in 1996 and 2011. These events can result from cascading failures when demand exceeds supply and automatic disconnections propagate across the network.
Reconductoring is the replacement of existing transmission lines with higher-capacity conductors on the same towers. Replacing a steel core with composite materials such as carbon fiber allows lines to operate at higher temperatures with less sag, potentially doubling capacity. A 2024 report found the United States behind countries like Belgium and the Netherlands in adoption of the technique.