World war is defined as an international conflict involving all the major nations of the globe. Typically, this term is reserved for the two major global conflicts that occurred during the first half of the 20th century. The definition of world war is a complex one, but in general, the conflict involved at least one or two of the major powers of the day. Read on to learn about both of these world wars, and what they had to do with each other and the lives they affected.

The world war began in 1914, and it was a massive conflict that lasted four years. The allied nations included the United States and Britain. Initially, there were two groups of nations: Central Powers and Allies. The Central Powers included Austria-Hungary, Germany, and Italy, while the Allies were France, Belgium, Great Britain, and Russia. Later, Japan, Romania, China, and the United States joined the Allies.

In 1916, the United States declared war on Germany. The United States cited the submarine policy of Germany and its alliance with Mexico to justify the action. The Allies were Russia, France, Great Britain, and Belgium. The United States joined later. The allied countries lost their cities and industries, and millions of people were displaced. This war also led to the rise of the Soviet Union and the Communist Party. The Allies helped the Allies win the war, and reshaped the global balance of power.