The right side or the left

UnavngivetTraffic can be quite complicated.

Some countries must keep to the right on the way other countries to the left
there are many theories, but none seems plausible to
why there is a difference.

In the very old days when traffic was by foot or on horseback
is the explanation that people stayed the left side of the road
to keep the hand with the sword free, facing the other traffic
if it should be necessary to pull the sword
but why then switch to driving on the right ..?

Some stories or myths
gives the french emperor Napoleon all the blame
because he was left-handed.

But it does not stand with the fact
that many countries introduced right-hand traffic
many years before Napoleon was born.

Is there any logical explanation at all
or is it just another example of politics ..?