So then when driving in about 25% of the countries, keeping on the left is correct whereas when driving in the majority of other countries, driving on the right is correct"
Well, according to my link: in 1773 an increase in horse traffic forced the UK Government to introduce the General Highways Act of 1773 which contained a keep left recommendation. This became a law as part of the Highways Bill in 1835.
Reasons to travel on the right are less clear but the generally accepted version of history is as follows: The French, being Catholics, followed Pope Boneface's edict but in the build up to the French Revolution in 1790 the French Aristocracy drove their carriages at great speed on the left hand side of the road, forcing the peasantry over to the right side for their own safety. Come the Revolution, instincts of self preservation resulted in the remains of the Aristocracy joining the peasants on the right hand side of the road. The first official record of this was a keep right rule introduced in Paris in 1794
OK, that explains the UK and France but what about the rest of the world ?
Britain's imperial expansion (all of the pink bits on old maps) spread the keep left rule far and wide. This included India, Australasia and much of Africa (Although many African countries changed to the right later when they became independent).
France also had quite an empire after the revolutionary wars and the keep right rule spread through much of modern day Europe and to colonies such as Egypt. The connection with the USA is thought to be General Lafayette who recommended a keep right rule as part of the help that he gave the Americans in the build up to the war of Independence. The first reference to keep right in USA law is in a rule covering the Lancaster to Philadelphia turnpike in 1792.
But what about Japan ? well in the 1850's Gunboat diplomacy forced the Japanese to open their ports to the British and Sir Rutherford Alcock, who was Queen Victoria's man in the Japanese court persuaded them to adopt the keep left rule.