The earliest wars were between groups of people called tribes. Tribes fought over thing like land,resources, and food. Later during the rise of the Roman empire wars were fought between the republic and the emperor. later guns were invented in china in the 1200s. Guns later became popular in Europe. In 1775 A war broke out between the American colonists and the British empire. In 1776 The USA was formed. and in 1900 Machine guns were invented. In 1914 World War 1 Broke out. World War 1 was the first war with machine guns as well as Tanks were introduced during world war 1.In 1940 World War 2 Started. the cause of World War 2 was that in 1939 Europe started a war and in 1940 it became a world war. After world war 2 the cold war happened. The cold war was a war between The USA & The USSR. [Today USSR is Russia] The USA won the cold war. after the cold war there were not many wars just small fights.