True; in many ways, the world has become smaller, thanks to the internet. However, things would diverge rapidly if we go interstellar, unless we somehow break physics or quantum magic can be used for instant communication / travel. The Expanse explores a nearer future where humanity has colonized our solar system, and already there's big tensions there.

One part of mutually assured destruction was that nuking the shit out of one country would cause a global nuclear winter which would / could kill 90% of the population - even without retaliation. That's not as much an issue if there's a healthy self-sustaining colony on e.g. Mars. Nowadays what keeps the world reasonably stable is mutual trade dependency, up to a point anyway.