War is organized, large-scale fighting between countries, groups, or armed forces. Unlike a playground fight or family argument, war involves armies, weapons, and battles that can last for months, years, or even decades. Countries go to war for many reasons: to defend their territory, to gain resources or land, to protect their allies, or because of deep disagreements about how people should be governed.

Throughout history, wars have shaped the world we live in today. The American Revolution created the United States. World War II helped end the spread of fascism in Europe and Asia. Some wars are fought to protect freedom and stop aggression, while others begin over misunderstandings or the ambitions of ruthless leaders. Wars can be incredibly destructive, costing millions of lives and devastating entire cities, which is why nations work hard to resolve conflicts peacefully whenever possible.

As a verb, war means to fight a war or to struggle fiercely against something. The word also appears in phrases that have nothing to do with actual fighting. A war of words means a heated argument. When someone declares war on poverty or a war on crime, they're committing serious effort to fighting a difficult problem. You might have a food fight at lunch, but calling it a food war suggests something bigger and more chaotic than just a few thrown peas.