Russia supplies Europe's natural gas . In fact 50% of Russia's immense production goes to Europe which is up to 34% of Europe's supply.
80% of that natural gas goes passes though Ukrainian pipelines. One of the first things Ukraine would do to pressure Russia to call back its troops would be to turn off the gas.
It is quite probable that gas is about to get far more expensive, and those other countries that supply the world's gas will see their GDP lifted. ie Qatar, Norway, Canada.
Shorting the Ruble is another good option to take advantage of recent events. In either case, things are quite tense and let's hope things don't get out of control.