Propaganda posters encouraged the public to join up and do their bit for King and Country.
The Government needed to recruit lots of soldiers and wanted people to work together. So what the public thought about the war really mattered.
They tried hard to persuade people to think in a certain way. This is called propaganda.
Posters were printed that made the army look exciting. Other posters told men it was their duty to join and they would feel proud if they did.
This BBC Schools site provides lots of really useful information and illustrations detailing WW1 propaganda.