What was the significance of the Russian cultural backdrop in "The Deer Hunter"?

There is no evidence that Russian Roulette had its origins in Russia, so that seems a superficial connection. It was probably chosen, as you suggest, partly because of its prevalence in the West Pennsylvania steel towns and partly because it is so heavily ritualistic and ritual is a theme of the movie - a Wedding, the dances at the Wedding party, hunting trips, men drinking together after work, a funeral, people gathered to gamble, the brutal rituals of war. (David Nolan, The Slow Review)

The original idea for the movie came from a script called The Men Who Came to Play which was set in Las Vegas (Wikipedia). This was combined with ideas from the plot of The Best Years of Their Lives, which chronicles the lives of three veterans returning from WWII to smalltown middle America. (Nolan) I have yet to find an interview indicating why the director Michael Cimini or the screenwriter Deric Washburn chose the Pennsylvania steel town to begin with. One can only guess - the likely camaraderie of steel workers, the small town environment where people grow up together into adulthood, the gritty color/non-color of steel factory backdrop which foreshadows the war setting, the Russian Orthodox religious connection....

The Deer Hunter is a multilayered allegory in four parts.

The first part depicts America before Vietnam when the Russians were perceived as the threat but in fact weren't hence the wedding. The send off identifies the confidence and naivety of both those going to the war and the Americian public and the state of the country "you're just too good to be true, can't take my eyes off of you".

The hunt identifies that in the end success depends on the motivation, preparation and skill of the individual, thus the friend who forgets his boots sequence and hunt.

The Vietnam sequence shows the War as a gamble where there were three outcomes, those who didn't return, those who returned maimed in body or mind or both and those who returned wiser but more cynical.

The final sequence depicts America after the war, the happy confidence lost forever.

The orthodox faith (by it's very name) is rich with ritual and order. I think this part of the film is important as contrast to the chaos and horrors of Vietnam. The first part of the film showed people living tough lives in a hardscrabble environment. The church served as a stable axle in their lives, a reference point of sanity from which the war veterans would later become untethered. I agree with the previous comments, there's no meaningful connection of this first act of the film to Russian roulette.

I think that it also ties in with a larger theme in the film, one that was not necessarily intended by the filmmakers.

The Vietnam conflict was a pointless war that the US didn't win, and it was played out within the context of the larger Cold War between the US and the Soviet Union (with China also a player). The war was about fighting Communism. The irony is that the men who go to the war are Americans, but they happen to be of Russian descent.

In one scene, Nick is sitting on a balcony in a hospital in Saigon when a doctor comes to verify his identity. He is "shell shocked" and clearly suffering from survivor's guilt having been rescued by the helicopter while his two friends fell back into the river. The doctor calls him by the Russian name on his record. He doesn't answer until the doctor asks him if his name is Russian. He says "no, it's American."

The point here is that these were hapless, working class Americans from all backgrounds who were sent to this futile war to fight and suffer and die for the benefit of larger powers involved in an ideological and global economic/political struggle. The Russian Roulette isn't Russian, but its name makes us think of Russia. And it is a deadly game of chance that is played, ultimately, by people who exchange money as bets on human lives, much like the powers that control wars.

I agree with all responses regarding rituals and would add one thought.

Screenwriters often seek to "bookend" scripts. THE DEER HUNTER's bookends are, of course, strong life rituals, ceremonial in nature - stronger and more basic than the scripts interior, or middle, rituals of hunting, drinking, etc. The opening bookend is the religious maritial ceremony, one of life's most basic rituals. The script's ending bookend is the funeral ceremony, perhaps the strongest ceremonial ritual. Bookends lend added strength to an already powerful script.

I think it showed the bonds of all the friends. So with church, drinking, work, hunting, and even war, the friends did everything together. It also hinted at De Niro's character's disdain for the religious rituals. This goes on to shows us that he is not like the others.

I don't know my initial instinct was the confusion of nationality was to drive home the universality of the story. The motivations of the characters were stripped down to the basics to show our fundemental human natures devoid of judgement based on nationality or ideology. They were from A working class community that idealised "patriotism" without understanding what that is, who generates it and for what purpose. Ultimatly it's only the often pubically hidden compassion that redeems the characters.The tragic rendition of god bless america at the end was a bleak condemnation of humanity that even through the horrors the characters personally suffered they still couldn't or wouldnt see through the horrifically manipulative illusion that other working class people,that never would otherwise have met you, are your mortal enemy.