Not necessarily. I think Ecuador has proven that a military coup isn't necessary. Not like it can't happen it Brazil (it's happened more than once), but it doesn't have to. If you can get enough centralized loyalists, you can start purging the corrupt politicians in your local power centers and push out from there. You also need law enforcement on your side. The president of Ecuador was actually negotiating with the cartels, until they decided that he was going to be reluctant to give them more shit, so they launched a terror campaign that killed over 100 people (IIRC) in the capital city. That's when he decided he'd had enough and went to war with them.