The Second World War began in the year 1939, specifically on September 1, when Germany invaded Poland. This act of aggression led to Britain and France declaring war on Germany two days later, marking the start of the global conflict. Over the course of six years, nearly every major nation became involved, resulting in widespread devastation and reshaping international relations. The war was characterized by significant events such as the Holocaust, battles across Europe and the Pacific, and eventually led to the establishment of the United Nations in hopes of preventing future global conflicts.