Break off = end; stop abruptly
Nobody knows why Alice decided to break off her engagement to Benjamin.
He broke off in the middle of his speech.
Break away (= become separate)
The boy broke away from his friends.
Break down = fail to work; go wrong; prove to be useless
My computer has broken down.
Break something down = use force to get it down
As she refused to open the door I had to break it down.
Break into = get into by force; start something suddenly
You can break into a fort, but not into a heart.
She broke into tears. (= suddenly started crying)
Break in on = interrupt; burst suddenly into
Break out = begin suddenly
War can break out any time.
Break up = come or smash into pieces; scatter
She broke up the chocolate bar.
That argument broke up their friendship.
Police used tear-gas to break up the mob.
Break the back of = finish the greater or more difficult part of a piece of work
Break the ice = overcome reserve and get conversation started