The Roman Empire walked to the left, actually. Legions marched on the left. As most people are right-handed, they would carry shields on the left and reduce the surprise of an ambush.
Also, in medieval England, castle staircases rotated clockwise, upwards, so if you're defending you have the advantage of striking from above without throwing your weight the wrong way. Knights also rode on the left of the road, so they could swing with their sword at incoming assailants. (way cooler explanation, right?)
Also, many (currently right-hand traffic) countries adopted left-hand traffic before the standardisation. The Austro-Hungarian empire had LHT, as did Norway, Sweden, all of the British Isles, all of the overseas empires (British and Portuguese, for example).
Train traffic is also predominantly (worldwide) left-handed.
Also, in medieval England, castle staircases rotated clockwise, upwards, so if you're defending you have the advantage of striking from above without throwing your weight the wrong way. Knights also rode on the left of the road, so they could swing with their sword at incoming assailants. (way cooler explanation, right?)
Also, many (currently right-hand traffic) countries adopted left-hand traffic before the standardisation. The Austro-Hungarian empire had LHT, as did Norway, Sweden, all of the British Isles, all of the overseas empires (British and Portuguese, for example).
Train traffic is also predominantly (worldwide) left-handed.