Judo is Judo. Sambo is not "russian judo".
You could say sambo is one of the first structured Mixed Martial Arts.
And Sport sambo is one of the competitive variants that originated from military/self-defense sambo - the other one being Combat sambo.
Sambo mixes various different wrestling/grappling and striking styles from Eurasia. Judo, jujutsu, grecoroman wrestling, freestyle wrestling, various forms of folk wrestling - mongolian, georgian, and in an old diagram, i even remember seeing swiss wrestling included (and i didn't even know that it existed)-, karate, aikido, box, etcetera.
Of course, it shares techniques with many other styles, even if it was not one of the styles it took from to form it's bases. There's only so many ways you can break someone's leg and arm, and there's only so many ways you can hip-throw someone or choke someone out. So no surprise, sambo may look like wrestling, judo, box, karate, jujitsu or whatever to the untrained eye.
I'll see if i can take a photo of the diagram of the structure of Sambo that is posted at the gym i train at, because it's very complete and understandable.
And, Combat Sambo is done in many other places other than the former USSR.
Russia, Ukraine, Belarus, Germany, Japan, Czech Republic, Bulgaria, Mongolia, Venezuela, USA, Mexico, etc.