Napoleon changed this habit by ordering his troops to march head-on into his enemies to disarm them, and forcing the countries he conquered to conform to his new French practice. By the turn of the 20th Century, when motor carriages were taking their first spluttering ventures out on to the roads, most of the world still drove on the left. In the USA, for example, the dominance of the Ford Model T (accounting for half the cars on American roads by 1910) eventually forced the Americans to drive on the right, with Ford switching its Model T production from right-hand-drive to left-hand-drive in 1908, and Cadillac and most other American marques doing the same from 1916 onwards.
In Europe, most cars were built with right-hand steering only, this being the case for prestige sporting French and Italian marques such as Bugatti, Delage, Talbot, Maserati and Lancia right through to the late 1950s. This resistance to change came from the fine motor racing credentials of these marques, where right-hand-drive is the norm due to most motor circuits being clockwise.
Between the first and second world war, most of Continental Europe gradually switched sides, with the former-Czechoslovakia, Austria and Hungary (in 1941) being the last to change, under the influence of Hitler. Under its war-time occupation, The Channel Islands was also forced to switch to driving on the other side of the road, only to change back once the hostilities were over.
Bizarrely, up to the mid-1930s, in Italy, the socialist-controlled cities of Rome and Napoli drove on the right, whilst Conservative cities such as Turin and Milan drove on the left! Today, all of Europe drives on the right, with the exceptions of the UK, Ireland, Cyprus and Malta.