The easy way out would be that these bots were created in response to all the preparedness that became the norm after Russia pulled their crap during the war. Somehow the bots got out of control and now turned against the people.
Another could be that it is Russia who sent these bots into the country. They ran across Finland and are taking over the north one country at a time.
3rd could be technomancy like the Wolfenstein and Hellboy universe. Arcane occult rituals bringing life and malevolence to non living machines.
Cooler still would be a Terminator situation ala skynet. This has happened all over the world.
Finally the best. As with anything ever. ALIENS!. Yep throw in Crazed E.T.s who are after our precious resources like water, air, and mayonnaise. All the natural resources needed for life.