Agile: history and theory crash course
Channel: makingthematrix
Date: 2019-10-29

The history and theory behind the most popular approach to team work in software development, boiled down to a few minutes. If you want to know more, read the Agile Manifesto: https://www.agilealliance.org/agile101/the-agile-manifesto/
Afterwards, google the names of the signatories or read about them on Wikipedia. You'll find out what parts of the Agile movement they are mostly involved in:
Ken Beck - Extreme Programming
Ken Schwaber, Jeff Sutherland - Scrum
Ōno Taiichi - Kanban
Martin Fowler - code patterns, refactoring
Robert C. Martin - SOLID principles
and many others who you may know as Agile coaches, team leaders, and authors of books and articles on software development.

Also please check the AgileByExample channel: https://www.youtube.com/user/AgileByExample
AgileByExample is an Agile conference happening every year since 2011 in Warsaw (Poland). They have tons of videos from their presentations, discussing in detail what I try to summarize in a few minutes.

Background music:
Winter Night, Summer Day by Beluga Ten (c) copyright 2019 
Licensed under a Creative Commons Attribution Noncommercial  (3.0) license. 
http://dig.ccmixter.org/files/Beluga/59738