In today's globally-connected financial system, it's pretty easy to send money from one place to the next, across most of the planet -- and that's all thanks to a system called the Society for Worldwide Interbank Financial Telecommunications, or SWIFT. Many people outside of the world of finance only heard about SWIFT recently, when the US and Europe declared they'd remove Russian banks' ability to access the system. What does that mean, exactly? Why was it described as a 'nuclear' option in economic warfare? And why did some European countries hesitate to pull the plug?