I'll be happy to do that.
The United States and Australia both considered this within the last four years and turned it down. The United States Supreme Court declared that once an individual in the United States has citizenship it cannot be revoked. It's for life in perpetuity and the United States has stayed committed to that. The sister country...I'm not 100% sure what the language “sister country“ means, or what counts there. There are approximately 14 European countries that allow revocation in cases of treason or terrorism. In most of those countries it has never been used. The most sister-like countries that have it are Belgium and Denmark. In both cases those are recently constructed, but mostly we're looking at states like the ones that I listed—that wasn't for rhetorical purposes—Lithuania, Estonia, Cyprus, etc.