In short, it's an Anime where countries are personified as humans and they reenact history (mainly World War II) in hilarious ways. And their characters are very stereotypical. For example, America loves hamburgers, Italy's obsessed with pasta, etc etc etc.
Hetalia Axis Powers - Incapacitalia is a popolare Anime series based on the webcomic da Hidekaz Himaruya. It features anthropomorphic forms of the world's nations and reenacts events in the history of-