France conquered many countries at than time, and so these countries drove on the right. But France didn't conquer England, so England kept its custom of driving on the left.
In the twentieth century, there was a trend to the right. Many cars were made for driving on the right side of the road. As recently as 1967, Sweden changed its laws. Now people in Sweden must drive on the right.
So right or left just follow the customs of the country where you are-and be sure to drive carefully on that side!