Russia and Ukraine

[Thumpalumpacus]

Federal government is funded by American taxpayers. In case of insurrection it will lose its revenue and won't be able to do anything.

This ignores the fact that aside from the self-employed (a small minority of tax-payers), Federal taxes are collected by payroll deductions, meaning that unless said taxpayers quit their jobs, the Feds receive a constant influx of money, and military paychecks roll out on schedule.

It's soldiers not insurrectionists that need banks and ATMs which don't work when power lines are destroyed.

Unless you're destroying powerlines in DC, you're not eliminating the disbursement of military salaries, which are by law nowadays by direct deposit. As for the local ability of soldiers to get money from local ATMs, they don't need to in the field, as they're fed and supplied by the logistics of the military. They are also often paid a per-diem, in cash, for daily needs not supplied by the logistics train.

Rebels, on the other hand, must pay for or seize their gas, ammo, food, and so on. By identifying those civilians involved in armed insurrection, it is quite easy to freeze their bank accounts, upon which they will be relying.

So you'll have to strike at the financial system itself in order to hamstring a military response. And that has pretty robust defenses built-in.

This is not even addressing the military competence, or C³I, of the insurrectionists.

They couldn't disrupt anything in Vietnam and Afghanistan.

Apples and oranges. Your two examples feature nations of very different languages, ethnicities, and financial systems. Insurrectionists in America would be far easier to penetrate and debilitate precisely because it's easier to pass as an American in America. You're also ignoring the fact that most Americans would not see the American military as an occupying force to be fought, but rather the legitimate arm of governmental force.

It doesn't seem you've really thought this through.