"These days there's a war on, right? and, ages ago, there wasn't a war on, right?...How did we get from the one case of affairs to the other case of affairs?" 

This is taken from an episode of the famous TV series Black Adder Goes Forth, where the character Baldrick ponders how you go from a state of war to a state of not war and vice-versa. In this War Studies taster lecture with Dr Jack MacDonald, he explores this question as well as who gets to decide whether a state is at war, what happens when people disagree whether a war exists and why people care if they are at war or not.