Red lines in the Russo-Ukrainian War

The term red lines has seen use in the Russian invasion of Ukraine in 2022. It is a veiled threat of engagement intended to warn an opponent or observer not to interfere or undertake an action or behavior that would "cross the red line." On 21 April 2021, Russian President Vladimir Putin made a speech in which he repeatedly warned the West of red lines that Russia would not accept. The warnings were repeated on many occasions up to the date of the Russian invasion of Ukraine on 24 February 2022. In particular, Russia identified Ukraine's possible admission to NATO as a 'red line'. During a December 2021 phone call between U.S. President Joe Biden and President Putin, "Putin told Biden that Ukraine's bid to join NATO must be denied in return for assurances that Russian troops would not carry out an attack." NATO's General Secretary Jens Stoltenberg rejected Russia's demand that it reverse its 2008 pledge to allow Ukraine to join NATO. "NATO’s relationship with Ukraine...