The story I heard, which admittedly is probably apocryphal and the product of an active imagination, also included Napoleon. Prior to then generally people riding horses would ride on the left, because that allowed the normally right handed rider to use his sword on the side from which he would expect attack. Napoleon changed the rules in the countries he conquered to create confusion and disrupt transportation. Sweden and Norway and of course Britain (Australia, Japan ?) were not conquered so kept driving on the left. T was told this story before I came to North America, so I can only presume regarding historical driving patterns here.