What did Phillips mean by "when lions write history" in his introduction to Douglass's book?

If you consider the effects of the winners always writing
history, you can look at the way we overlook the actions of certain despots and
highlight those of others depending on who were the winners and losers.  How many school
children can immediately shout out the evils of Hitler but don't know about Stalin's
pogroms or the mass murders committed by Pol Pot with weapons supplied in part by the
good old US of A?  It is dangerous because those in power always get to skew things
their way to deflect blame, to influence society in rather powerful
ways.

One of the most difficult things to teach students is
the idea that history is not based on facts, but is based almost entirely on
interpretations of the facts and the actions of people in the past.  If we only allow
the winners to make those interpretations, it becomes easy to accept one viewpoint and
not raise objections.  There are people out there who say that our participation in WWII
was absolutely a mistake.  Of course the accepted view is that it was a moral necessity,
but without the other side, who would raise objections about our firebombing Tokyo or
interning Japanese citizens without any good reason to do so?  Without the other side
getting to have their input we move towards a 1984-like state where everything is edited
to fit with the vision of those in power.

This is certainly
not a new concept as Phillips points this out quite a long time ago but we are still
struggling with it today.