As WWII raged on, Hitler began invading other countries, and Picasso began to fear for the safety of the piece in Paris under Nazi occupation. He decided to loan the piece to New York's Museum of Modern Art, and it would eventually tour the United States. It became one of the most discussed artwork, as its meaning and value in modern society continued to be debated. It also raised sympathy for anti-Fascist causes. From 1953-1956, the piece toured Brazil before moving on to various European cities. It was then kept in a separate room in the Museum of Modern Art (MOMA) due to concern over its state.
By the time of the Vietnam War, the painting's room became a pace for peaceful anti-war vigils; that is, with one exception: in 1974, Tony Shafrazi spray-painted "KILL LIES ALL" on the mural, protesting President Nixon's pardoning of former US army officer William Calley for his role in the massacre at My Lai. The spray paint was quickly removed and all went back to normal.
In 1968, General Franco articulated his interest in having the Guernica sent back to Spain; Picasso, of course, wouldn't hear of it, and declared that he would only allow it back into the country when Spain was once again a republic. Unfortunately, this didn't happen until after Picasso's death in 1973, followed shortly by General Franco's in 1975. By 1978, Spain had become a democratic constitutional monarchy with a new constitution. Understandably, MOMA didn't want to return the piece, and it argued that the current Spanish government didn't fulfill the conditions of the republic that Picasso had specified in his will before the painting could be returned. It wasn't until 1981, under great pressure from outside sources, that MOMA returned the art work.