If you're having trouble connecting to Call of Duty: Black Ops III, you should first check Call of Duty: Black Ops III Server Status. If the status indicator for your platform is not green or an alert is present, you might encounter connectivity issues until service is restored and fully operational.

Is Call of Duty Black Ops 3 online only? Bo3 is not a multiplayer/online only game. It has a great campaign *this is just a personal opinion*and you can make a custom multiplayer game where you play with a few friends or you can practice against bots. Hope this helps you out.