If a country prints it's own currency in large quantity, at what point do they self-destruct?

One observation/question, but first, as you probably know, during wars one country can print it's enemy's currency in large quantity and "helicopter" drop it in enemy territory, in an effort to create hyperinflation and thus destroy it's economy. After pearl harbor Dec 1941 the US found out that Japan was planning to drop large amounts of US dollars. The US then took out the paper dollars and replaced them with dollars that had "Hawaii" printed on them. (google: Hawaii printed on us dollar bill). The US let the Japanese know they would drop fake Japanese dollars if Japan did went ahead, which they didn't. Germany printed the English pound during WWII and fake German Marks were dropped into Germany also.
Now the question: If a country prints it's own currency in large quantity, at what point do they self-destruct?