Break In Meaning

(transitive, of a horse) To tame; make obedient; to train to follow orders of the owner.

Example:   Someone broke in and stole his radio.
2013 June 18, Simon Romero, "Protests Widen as Brazilians Chide Leaders," New York Times (retrieved 21 June 2013):
  Thousands gathered at São Paulo’s main cathedral and made their way to the mayor’s office, where a small group smashed windows and tried to break in, forcing guards to withdraw.
  These shoes will be more comfortable after I have broken them in.
1877, Anna Sewell, Black Beauty
  Captain had been broken in and trained for an army horse; his first owner was an officer of cavalry going out to the Crimean war. He said he quite enjoyed the training with all the other horses, trotting together, turning together, to the right hand or the left, halting at the word of command, or dashing forward at full speed at the sound of the trumpet or signal of the officer.