World War II was the most widespread and deadliest conflict in world history, claiming 40 to 50 million lives, including roughly 6 million Jews executed during the Holocaust. In the wake of these atrocities, the phrase "Never again" became a reminder to not stand idly by while people are slaughtered. A memorial wall at the Dachau Concentration Camp in Germany reads "NEVER AGAIN" in 5 different languages. In the run-up to World War II, Britain and other nations appeased Nazi Germany and continued doing business with Italy as they invaded other nations. From the 1930s until 1941, the U.S. followed a policy of isolationism, a refusal to participate in conflicts or politics in Europe and Asia. This ended when Japan attacked Pearl Harbor.