Anything described as revanchist is connected to a political policy of reclaiming lost territory. A powerful country's revanchist actions often lead to war.
The noun revanchist was coined in the 1920s to describe Germans who were focused on reclaiming territory lost during World War I. As an adjective, it's used to talk about the political idea of revanche, or revenge in the form of taking back land that was lost in an earlier military conflict. Iraq's 1990 invasion of Kuwait is an example of a revanchist policy; the government claimed that Kuwait, autonomous since 1913, was actually part of Iraq.