1. Bitcoin absolutely could be taken over by a major world government forcibly.
2. Short of an outright takeover of the network, a few words from the US president could send the price of Bitcoin down by 90% or more, and an act of the US Congress or an executive order by the US president could send the price of Bitcoin down by 99%.
The best "intervention that a government could do is to destabilize bitcoin's economy by buying sizable amounts of cryptocurrencies and then selling those en masse. Which by then is going to cause a massive stir and would definitely trace the transactions back to them, ending with a massive backlash on their behalf. They could also go the beaten path and ban cryptocurrencies altogether and face the backlash now and hope that the people forget they love bitcoin, but when you have millions held on a stupid wallet that's not gonna happen.
You'll come to realize that bitcoin is as anarchic as you make it out to be. It was indeed made to combat governments and shit, but not so thiefs can steal money and then convert them to cryptocurrencies. Honestly speaking the anonymity aspect is just a byproduct of the fact that it is decentralized but I digress.
I hate preaching bitcoin but it's not as fickle as you think it is. Economically (scalability) speaking it's as strong as a twig but everything else is robust about this coin. Don't get it twisted.