Maxey is right. Also, the word "to" is a preposition meaning in a direction towards a place e.g. "She went to the end of the road" or towards a condition e.g. " He was nursed back to health" or towards an extent " The boat sank to the bottom of the lake" The word "of" is also a preposition. " Of" expresses the relationship between a part and a whole: Example: "the sleeve of his coat". '' Of " also expresses the relationship between a scale or measure and a value: Example " The shares had an increase of 5 percent".

A was the background to B = A was B's background A had a background of B = B was A's background A was the background to B = A was B's background (only one direction here) I can also say: ...a person with a background of B. B is the person's background.