Karmic Lessons v Karmic Debt

I have been reading about Karma today - a karmic debt always involves a very serious act where there has been violence and death perpetrated by one human being onto another, and may take many reincarnations to pay back ( bugger ).
On the other hand Karmic lessons are those basic to our evolution as human beings such as patience, love, trust, charity,etc.and may be learnt in one lifetime.
Our soul decides what lesson(s) we have to learn before we are reincarnated.
Reincarnation can therefore take centuries until the circumstances are just right for those lessons to take place or it can be immediate.
Then, it is up to us to choose the time and place for these lessons to be learnt as our life unwinds.
The lessons are there ready to be taken up - but we have freedom of choice, or free will,  to do so or to ignore.
That is why predicting the future is a fromidable task - As a reader, I always say to people that, some outcomes are easier to see coming ( or "on the cards " if you like ) as they tend to have a set pattern ( especially if repeated over and over during one's lifetime) but the circumstances by which you learn those lessons can vary greatly by the decisions you make.
Karmic debt may mean that you have suffered through an horiffic death at the hands of a perpertrator who then has to spend the next few incarnations "paying for his crime against another " and you, the victim, must learn to come to terms with the fears and emotions associated with the incident.
I wonder then, about those that went through World Wars 1 and 2 and may have had to kill or be killed and what of their debt, or lesson, in lives to come.
My understanding of karma is "what you reap you shall sow" ( to quote a Bible verse.)
It is not "an eye for an eye" - because in the end it all comes back to the greatest lesson for us all which is to learn how to love and be loved and you cannot do that by punishment, fear and retribution.