The US and UK introduced circular intersections in the early 20th century.  The US and UK adopted widespread use of rotaries in the 40's and 50's and while both countries found them to be less than ideal, the US walked away from them while the UK kept on tinkering. The offside priority rule (yield on entry) and smaller size with deflection on entry are the key operational and design changes developed by the British. The French and Aussies have just applied them more than the US. We're essentially importing the refined, safer grandchild of the east coast rotary, thus the preferred name modern roundabout. Look up Frank Blackmore.