This custom
comes from some centuries ago, when feudal lords rode on the left side, the
same side they carried their sword. When they found enemies, they could
unsheathe and defend themselves with their right hand.
Also, in
big carriages, when coachmen used the whip, they used to reach passengers travelling
on the carriage coming from the other side when they went on the right. So,
they decided to drive on the left side in order to prevent this problem.
Because of
that, in England and in other countries which were British colonies, like Australia
and India, people drive on the left side.
However, in
continental Europe, Napoleon Bonaparte changed this habit because he was
left-handed. He’d rather keep his left arm between him and his opponents and
so, he could manage his horse better. He repaired some roads in Europe and he
established the traffic flow on the right side.
From that
moment on, countries which are influenced by France drive on the right side,
while countries belonging to the British Empire drive on the left one.