You are referring to the dispute between Thomas Edison, whose system used DC, and Nikola Tesla/George Westinghouse, who used AC.
The physics have not changed. What has changed, as pointed out by Jim N., is the practicality of generating high voltage DC power in significant volume and then stepping it down to a safe voltage.
It is not exactly correct that AC is better for power transmission than DC. But it is very true that you need high voltages to efficiently transmit power. In the nineteenth century, the only practical way to step voltage up and down was to use transformers, and transformers require AC. But alternating current is subject to several types of losses that don't affect direct current. Power engineers have looked to DC transmission for a long time, but it wasn't until the 1970s when it started to come together: Rising fuel costs, greater demand (requiring longer transmission lines), and improved technology made DC transmission cost-effective for long transmission lines, particularly underwater cables. The equipment required to generate high voltage DC and convert it back to AC is much more expensive per kilowatt than transformers, so DC is only used when the cost savings from improved transmission line efficiency justifies the additional expense of DC.
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