Liechtenstein is a tiny principality sandwiched between Germany and Switzerland. A lot of Britons couldn’t easily find it on a map, so perhaps it’s not surprising that, as far as I know, we’ve never invaded it.
In the First Word War, because of Liechtenstein’s extremely close relationship with Austria, we weren’t quite sure what to do about it. So in the end we decided that while we weren’t actually at war with it, we were going to apply an economic embargo on it anyway.