Best movies I've seen this year--some common threads

I was pondering the best movies I've seen so far this year, and I realized that they all have a few things in common.  See if you can figure it out:

Bridge of Spies

Hidden Figures

The Zookeeper's Wife

A United Kingdom

Things I found in common:
-All take place in the recent past
-All are based on true stories
-All feature some aspect of politics
-All feature some sort of prejudice/segregation and the fighting of it
AND...
-All are based on books.

Yay for books!

Bridge of Spies is based partly on Strangers on a Bridge by James Donovan

Hidden Figures is based on Hidden Figures:  The American Dream and the Untold Story of the Black Women Mathematicians who Helped Win the Space Race by  Margot Lee Shetterly

The Zookeeper's Wife is based on The Zookeeper's Wife; A War Story by Diane Ackerman

A United Kingdom is based on Colour Bar;  The Triumph of Seretse Khama and His Nation by Susan Williams