What is War? - Definition & Causes

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  • 0:04 War
  • 0:27 Causes
  • 3:25 Casualties
  • 4:16 Lesson Summary
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Lesson Transcript
Instructor: Joanna Harris

Joanna has taught high school social studies both online and in a traditional classroom since 2009, and has a doctorate in Educational Leadership

Have you ever wondered why, after thousands of years, there is still warfare? This lesson goes over some causes of war, including imperialism, nationalism, resources, religion, and territory.


Wars have been fought since the beginning of time for a multitude of different reasons. Whenever leaders of nations cannot come to a peaceful negotiation to solve a dispute, other avenues are taken. Unfortunately, these different avenues often result in violent hostilities called war, where leaders pit their mercenaries or militaries against each other in clashes that can cost thousands or even millions of lives.


Let's cover some of the many different causes of war and take a look at some historical examples.


One reason for war is when one nation seeks to take advantage of another nation's natural resources. For example, imperialism is when a developed nation conquers or colonizes a less developed nation for trade or extraction. For example, in 1898, the United States went to war with Spain and took over Puerto Rico, Guam, Cuba, and the Philippines from Spain. Imperialism can also lead to revenge, and sometimes the exploited or wronged nation seeks retribution through warfare.


Ownership of land is a common cause of war. For example, think of all the wars in North America between Native American tribes and Europeans, and even the European nations themselves. In the Seven Years' War for example, England and France both coveted the Ohio River Valley, while England and Spain had long been in contention over Florida. With Native American tribes siding with either the French, Spanish, or British colonists, the melee was a truly global conflict. England emerged victorious, gaining Florida and control of the Ohio River Valley all the way through Canada.


Access to resources can also lead to war. For example, post World War I, Japan modernized their nation's military, which depended on gaining new sources of oil for their island nation. Japan also desired more room to expand their borders to accommodate their exploding population.

In the 1930s and 40s, Japan grabbed Manchuria (China), French Indochina (Vietnam), and the Philippines. This aggression prompted the United States to issue sanctions, including restricting the Japanese's access to American oil. As a response, Japan attacked American-held Pearl Harbor in Hawaii in December of 1941, and essentially spurred the United States to officially join the war on the side of the Allies against Japan.


Nationalism, or the extreme pride in one's own nation and culture, can be an instigator of war as well. Nationalism predicated the start of World War I. Europe and the Middle East looked much different in 1914. Austria-Hungary, the Ottoman Empire, and even Germany had different borders that all included ethnicities like the Slavs and the Turks who all wanted to be independent.

These ethnicities tried to break away from their larger and stronger parent nations. This led to the start of the greatest war the world had ever known at the time, which dragged all of Europe, the Middle East, parts of Asia, and eventually the United States into a four-year war that claimed the lives of millions.

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