This depends somewhat on how you define "Austria". Before 1918, more or less all of Czechoslovakia was part of the Austro-Hungarian Empire, although this state was often referred to simply as "Austria". When that empire collapsed in 1918, the new state of Czechoslovakia was created from the old imperial territory, specifically Bohemia, Moravia, and Slovakia. So while the new state was created from "Austrian" territory, it didn't really include any of what would be considered Austria in a strictly geographical or modern sense, i.e. the current version of Austria.