In Swift's liner notes, which she posted to Instagram, she talks in depth about the inspiration for some of her songs and characters, including her grandfather (yes, the same grandfather whose picture shows up in the "Cardigan" music video) "landing at Guadalcanal in 1942." Guadalcanal was a months-long campaign in the Pacific theatre during World War II, which was the first major land offencive by the Allies against Japan.
A lyric in "Epiphany" seems to evoke that wartime experience: "Keep your helmet, keep your life, son/Just a flesh wound, here's your rifle/Crawling up the beaches now."