Vietnam War.

Harry's P.O.V.
When Harry get's drafted into the war he is scared. He's scared until he see's the face of perfection after falling into the dirt getting off the army bus. When he falls the General comes running up asking if he's okay.
Louis' P.O.V.
When he see's a beautiful man fall out of the bus he runs over seeing if he's alright, knowing all well that people will question why he did it. He get's up smiling at the unknown boy holding out a hand "I'm General Tomlinson. Who are you?" He will never forget the gruff voice of the tall lanky lad. "Harry. Harry Styles."

Basically Louis falls for Harry as soon as he see's him fall off the bus.