Imagine a group of friends playing a game of tag. One friend starts showing off how strong and tough they are (Militarism), then they team up with some other friends to help each other (Alliances), and start claiming more and more playground space as their own (Imperialism), which makes everyone else feel proud and protective of their own space (Nationalism). Eventually, someone gets tagged and a big fight breaks out, turning the whole playground into chaos - that's how WWI started!