The historical context for The Lucky One is the Iraq War, especially soldiers returning home.

The book is about the effects of the Iraq war on a soldier and the ones he loves. 

The main character is Logan Thibault, who has been in the Marines. 

When he is in Iraq, he finds a picture of a woman and falls in love with her.  The picture is supposed to bring him good luck.  Back in the states, he finds the woman in the picture, hoping she will fall in love with him.  She eventually does, after he explains the picture.

Returning to the US is not easy for Thibault.

The structure of the Marines was based on threes.  …. He served three tours in Iraq.  Checking his watch, he noted that he’d been in Hampton for three hours, and straight ahead, right where they should have been, were three evergreen trees clustered together. (p. 51)

The book deals with the loneliness and isolation soldiers felt when returning from Iraq.  Like Vietnam, it was an unpopular war.  When Thibault returns, he feels so disconnected from civilian life that he obsesses over the picture and has to track down the woman in it.