GoPro Ride Through an Electron Beam Irradiator at Full Beam Power [video]

If there's a reason to assume otherwise, I've yet to become aware of it. Or are you getting at something more earthly in scope?

I always assumed they'd just use the gov't mandated encryption backdoor.

Then again, since the master code was 000000, it wouldn't really be to difficult to break without a backdoor

Okay, but if they can do that to our networks, why assume they can't about as easily do it to us?

There's a good deal of Turtledove in my perspective on this, yeah. His academic study of history lends a perspective few if any other authors in my experience share; my own study of the same subject, though entirely amateur, tends to make his counterfactuals seem more plausible rather than less, by which I infer both they and their consequences in his stories are drawn with scholarly care.

Seeing something occur that we thought was impossible tells us our understanding of physics is incomplete, which we already know. Seeing how it is done would probably tell us more, but we haven't. Until we do, we're guessing, and to assume FTL mastery confers godlike powers is as much an assumption as any other. Turtledove addresses this in the story that a sibling commenter mentions; I can also recommend that story, which rewards the reader with considerable entertainment while making its point about what can reasonably be assumed in the total absence of information.

The same goes for the sublight option, only a lot more so. Unless they have FTL communications, which I believe we also consider effectively impossible, by the time they get here anything they think they know about us will be wildly outdated, in technological terms at the very least. Possibly also in terms of the dominant terrestrial species, but we can be generous here.

We can be generous about their information latency because that only matters if they want it to. Any species which wants us dead and doesn't care what state the planet's left in - a reasonable assumption, if we're talking about them popping our nukes at us - doesn't need to come close to landing, or even to orbit, to do it; a kinetic bombardment in passing will amply suffice to depopulate Earth to more or less any degree desired. For subluminal interstellar travel to be even remotely feasible, even for an individually long-lived species, implies access to the kind of delta-V budget where the only limiting factor in such a bombardment is the time it takes to accelerate impactors, which may be zero if those are released before or during deceleration to match velocity with our solar system.

In the former or FTL case, we don't know how FTL works or even could, and we therefore can assume anything we like - with all assumptions at equal risk of bankruptcy. In the latter or high-sublight case, they don't need to be more clever to kill us if that's all they're after, and it may be unreasonably charitable to assume we would even get a chance to see it coming.

I don't see why or how the step 3 would happen. Even if NK nuked South Korea, and even if theoretically US responded with a nuclear strike(and that is already really stretching it), why would other superpowers respond with their own nuclear strikes? China would be super unhappy, sure, but would they attack US with nukes over destruction of North Korea? I don't see it.

I can see Pakistan and India exchanging nukes, but why would anyone join in that?