1. Georgia started it. Attacking a state by which Russia pretty much considered it's residents citizen's was stupid.
2. The missile defense system in Poland was in the works long before this action broke out. Russia has been against it from the start. The US claims it's to protect countries from rogue states like Iran from launching missile attacks. Given the history Russia has had in wars, it's not surprising that they have an issue for it.
3. Yes, it is scary how cold war rhetoric is suddenly coming back to the forefront. Russia knows that the US is in no position to do anything but political posturing. Considering how we have acted with the international community in general, it's not a surprise they are being this bold.