Why was alternating current more useful than early direct-current systems for long-distance power transmission?

Alternating current (AC) became more useful than early direct current (DC) systems for long-distance power transmission primarily because AC allows for the efficient use of transformers.12

In electrical transmission, power loss is proportional to the square of the current. Early DC systems operated at low voltages, which necessitated high current levels and resulted in significant energy loss over distance. Because DC voltage was difficult to change at the time, it could not be easily stepped up for efficient transmission.13

In contrast, the periodic variation of AC enables transformers to step up voltage to very high levels while simultaneously lowering the current. By transmitting power at high voltage and low current, energy loss due to resistance is greatly minimized. Once the power reaches its destination, transformers can easily step the voltage back down to safe, usable levels for domestic and commercial consumers. While modern technology has since enabled efficient long-distance DC transmission, AC’s ability to easily transform voltage was the decisive factor that allowed it to supplant early DC grids.123