What is trauma/complex trauma/C-PTSD and why is it more common than we may think?

Here are links to material explaining trauma and how we might be affected by it.
 

Trauma is a neuro-physiological process by Julia Vaughan Smith
https://www.juliavaughansmith.co.uk/blog/trauma-is-a-neuro-physiological-process

"What is CPTSD?" Simple Definition - Complex Post-Traumatic Stress Disorder
By Richard Grannon, The Spartan Life Coach
https://www.youtube.com/watch?v=vwp52uv9LMY

How Childhood Trauma Leads to Addiction - Gabor Maté (by addiction Gabor Mate also means internet, sex, relationships, shopping, work, eating and more)
https://www.youtube.com/watch?v=BVg2bfqblGI

Trauma typology by Pete Walker
http://www.pete-walker.com/fourFs_TraumaTypologyComplexPTSD.htm

Emotional neglect by Pete Walker
http://www.pete-walker.com/pdf/emotionalNeglectComplexPTSD.pdf

Codependency, Trauma and the Fawn Response by Pete Walker
http://www.pete-walker.com/codependencyFawnResponse.htm