President Obama began to ease the embargo restrictions in 2016, allowing for travel and investments. It was Trump, in 2017, who reinstated the embargo in full. Probably just because Obama relaxed it.

Because the people there didn’t allow US capitalists to exploit them and their resources; because the people started to organize themselves and their resources around public interest; because they were voting in leaders who didn’t allow US elite to exploit them.

And so they must be punished.

Here's Practical Engineering explaining how it almost happened in Texas. he also goes into why starting from a black start is so hard

Article doesn't say, but one plausible scenario:

A big power plant goes down and other plants have to pick up the load. Load exceeds capacity of remaining plants and they shut down (or breakers blow, etc). Repeat.

Power plants also need energy to start up (black start), and if there's no grid energy to power those ancillary systems, or if the power plant doesn't have on-site auxiliary generators to provide black start capability, they're down until they can get power again from elsewhere.

Base load plants (coal, nuclear) don't throttle up and down quickly for changing loads. For quick response, we use peaker plants which are typically natural gas powered turbines and can respond quicker (grid batteries are, thankfully, replacing these in some cases).

That's grossly over-simplified but it's more or less the gist of it.

Cascade failure maybe? Sudden loss causes other plants to try to pick up slack, overloading one of them, which puts even more pressure on the rest until they all fail?

For a historical analogue check out what happened in Italy on 28. September 2003. One international line in Switzerland sparked to a tree, and got shut down, that caused a cascade where the other lines to France were overheating and getting shut down a few minutes after, and Italy didn't manage to shed enough load in time to keep up their frequency internally, then everything shut off when it drooped low enough. Took them 18 hours afterwards to get the whole grid back online.

Electric grids are really tough to get back online from what I've read. Rolling blackouts help keep things online, but if the whole thing goes down at once it's tricky to get all the generators on the same timing for their 60/50 Hz transmission lines.

If demand exceeds supply, the whole grid will fail as the voltage/frequency drop trips all sorts of safety systems meant to protect the grid and the devices connected to them. Normally the supply and demand are continually balanced to avoid this.

If a major plant goes offline and you don't shut down equal demand at the same time (usually by disabling entire neighborhoods) then this is the result.

https://en.m.wikipedia.org/wiki/Northeast_blackout_of_2003

The blackout's proximate cause was a software bug in the alarm system at the control room of FirstEnergy, which rendered operators unaware of the need to redistribute load after overloaded transmission lines drooped into foliage. What should have been a manageable local blackout cascaded into the collapse of much of the Northeast regional electricity distribution system.

Not a plant but another example of something that should have been small causing massive outages. From what I know talking to people who've worked for the province's grid operator, it's a massive job to keep everything going.

That's how power works, you miss your requirements by even a little and you can get cascading failures if you haven't engineered things well and your guys aren't sharp.

Power engineering is not something casual, it's brutal and if you aren't on your toes then your toes will leave black sooty marks where they were.

We spend insane amounts of money keeping things going, Cuba probably cut corners and couldn't do upgrades due to sanctions/embargoes.