World War 1 vs World War 2: Causes, Deaths & Key Differences

The main difference between WW1 and WW2: WW2 was 4× deadlier (70–85M deaths vs 20M), involved twice as many nations (60+ vs 30), and introduced nuclear weapons. WW1 (1914–1918) was triggered by a web of alliances after Archduke Franz Ferdinand's assassination; WW2 (1939–1945) was caused by Nazi Germany's expansionism — and was itself partly caused by WW1's punitive Treaty of Versailles.