A nuclear conflict could be sparked by either side making a calculated decision to use nuclear weapons (and you're fooling yourself if you believe the US is any less trigger happy in that regard than Russia), but it can also be sparked by either side due to a mistake resulting from a technological malfunction, miscommunication, misunderstanding or miscalculation, as nearly happened many times during the last cold war. The more things escalate, the more likely both such possibilities become.
And, clearly, things are escalating.
And that's just Russia; tensions are rapidly escalating between the US-centralized empire and China as well. In an article for Antiwar.com titled "There’s Little More Washington Can Do To Convince China To Invade Taiwan," Andrew Corbley describes the frighteningly extensive provocations the US has been pouring into another massive geopolitical powderkeg just in the past few weeks.
Reading by Tim Foley.