Final answer:
World War II, involving Western European countries, the US, Russia, and Japan, was the deadliest global conflict in history, starting at different times according to regional perspectives and resulting in substantial political and societal changes worldwide.
Step-by-step explanation:
The global event that saw the involvement of countries like those in Western Europe, the US, Russia, and Japan is known as World War II. Occurring between 1939 and 1945, this conflict emerged as the deadliest in history due to its vast scope, involving multiple continents and resulting in up to eighty million deaths. Notably, World War II began in Asia with Japan's 1937 invasion of China, whereas Western European narratives usually mark the start with Germany's 1939 invasion of Poland, and the United States history tends to focus on the Pacific theater starting from the Pearl Harbor attack in 1941.
Key participant countries included Western-aligned nations such as Greece, Norway, Iceland, the United Kingdom, France, Denmark, West Germany, Italy, Turkey, Netherlands, Belgium, and Luxembourg on one side, referred to as the Allied powers. Opposing them were the Axis powers, which included Germany, Japan, and Italy. World War II significantly influenced global politics and its aftermath shaped the modern world, igniting nationalist movements in colonized regions and leaving an indelible impact on international relations and collective historical memory.