The content originally appeared on: CNN (CNN)As the war in Ukraine has passed the six-month mark, US and European officials say Ukraine has successfully used a method of resistance warfare developed by US special operations forces to fight back against Russia and bog down its vastly superior military. The Resistance Operating Concept was developed in 2013 following Russia's war with Georgia a few years earlier but its value was only realized after Russia's invasion of Ukraine's Crimean peninsula in 2014. […]