solved What were the Causes and what was the Trigger of

What were the Causes and what was the Trigger of World War 1? Moreover, were the causes justified reasons for war? Lastly, do historians and you agree on why the war happened in the first place?
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To set the stage, start by viewing the following documentary (35:32 min) and include the causes listed and reasoning discussed in your reply – see: History of World Civilizations – Causes of World War I:
World History – Causes of World War I (Links to an external site.)
Please use your textbook, a reputable academic source of your choice (you’ll need to name at least two historians with differing opinions for your last section of the question.