During World War II, Adolf Hitler used propaganda to convince the German people that Jews were evil. His invasion of Poland was also preceded by propaganda.
More generally, propaganda is often used in the lead-up to any war (or genocide). A well known example from the past decade was the Coalition invasion of Iraq, which was preceded by propaganda about Saddam Hussein possessing weapons of mass destruction, allegations which have since been proven false.
Over the past decade, controversy has arose surrounding the role of video games in propaganda, with critics raising concerns over the role of military first-person shooters (many of which happen to be set in the Middle East) as propaganda tools for various governments such as the US or UK.
Some of the most famous video game critiques of propaganda is Hideo Kojima's Metal Gear series, most notably Metal Gear Solid 2: Sons of Liberty.