I think cotton fabrics have always been cheaper in the U.S. because we have the land and climate to grow cotton on a large scale, plus the mills for manufacturing thread and fabric. I think the U.K. has to import most of its cotton. I would imagine places like Australia and New Zealand have the land and climate to grow cotton, but maybe not the mills, so they end up exporting a lot of raw cotton.
Didn't cotton prices go up dramatically in England during the revolutionary war with the states? I think that was because England lacked raw cotton.