Despite primarily focusing on the US, The Walking Dead‘s outbreak seems to have had a worldwide effect, with the franchise revealing some major details about the rest of the world throughout its tenure. Having run for 11 seasons, the original show never really deviated outside of America, opting to put the focus on the survivors and their attempts to rebuild society, rather than the origins of The Walking Dead‘s zombie virus. Naturally, things like everyone being infected and how to properly kill the undead were established, but the full extent of the apocalypse remained a mystery for some time.

https://screenrant.com/the-walking-dead-rest-of-the-world-zombie-outbreak/