Where do you think Russia would ally itself if there would be another war?

Russia still has strong ties was various members of the CIS (former Soviet states), especially Ukraine and Belarus. In any region conflicts, it is highly likely that it would support these nations.

While the US and Russia have both condemned each others military operations since the end of the Cold War, they have also kept out of each others way. An example would be the 2008 war with Georgia. Despite Georgia being an ally of the US, the US did little more than condemn Russia. Likewise, the US engaging in sanctions against Iran (which is supported, at least in part, by Russia) has done little to provoke a reaction from the Russians beyond diplomatic talks.

It is not likely that we will see another war on the scale of WW2, as the world has probably learned its lesson. However, Russia and China have close military ties, and would likely support each other in a global conflict. But in the war against rouge states and militant Islamic extremists, the Russians hate extremists just as much, if not more than the Americans (consider the multiple terrorist attacks that have been perpetrated in Russia over the past 10 years, and the situation in Chechnya), and would in all probably, ally themselves with the United States if the situation presented itself.

Russia will only do what benefits Russia, just like the did in WWII with first helping Germany, and later the Allies. Even in the Pacific, they made several treaties with Japan before declaring war.

It depends on the reason for the war, and the parties involved. Russia has fought both with and against the US in the past.

Entirely depends on which countries are involved in the war.

(Remember - Russia and US were allies in WW2)

They would stay out of it if they knew what was good for them

against the us for sure