There is not much need for an armed invasion of the US in my opinion and we wont see that anytime soon. What would China or Russia do with the US? They would never be able to hold any major part of it. Look how hard it is for the US to hold Afghanistan (a country that pretty much runs without proper electronics).
I think China will become the new leading nation over the next 10 – 20 years and I dont know what will happen to the US. For Europe I also have no idea what will happen to the southern parts of Europe. Their productivity is pretty terrible but most people have lived a pretty good life despite of this. With ongoing globalization those states are in for a hard time as well. Northern Europe along with Germany either gets dragged down by all of this like everyone else or they split and team up with new allies (I doubt with Russia, but maybe with China…).
Overall I think we don’t have to be worried about conventional wars too much (unless Putin does something really stupid which he is probably capable of). The biggest thread are civil wars, separatist movements or rebellions that get shot down by the government (as it happened in Syria).
We should expect that the powers are shifting and western nations will not lead anymore in the coming decades. It will be interesting to see how people in the US and Europe deal with that. Its not easy to slide into poverty,
Alea iacta est ("The die has been cast")