Arminians and other Libertarians are concerned with determinism, the proposition that all of our actions are made necessary by God in some way. We are concerned because determinism seems to make God the author of sin.
The compatibilist wants to show that we can still be free and responsible for our own actions and they can be determined. David Hume, a skeptic philosopher, tried to show this is the case on a naturalistic framework. Theist determinists adopt some of Hume’s arguments and augment them in order to argue that it is possible that all our actions have been pre-determined, but we freely do those actions and are therefore responsible for them. There have also been other attempts at trying to show that this is possible.