Nation-states, city-states, empires and Kingdoms have interacted with each other in a similar way since the end of the thirty years war. An example could be China, Africa, India, and Ancient Greece; they got involved in economic relations, established embassies and helped each other or fought in war. After 1648, we could how the development of the international system became a "globalized system". World wars impacted in a global scale, although world war 1 and world war 2 took place in a 20 year difference, they also have their similarities besides geographic place. The changes in technology affected the way they fought; machine guns, airplanes, and submarines all took part during this fighting. World War 1 began on July 28, 1914, when Austria-Hungary declared war to Serbia. War finally ended in the late fall of 1918, after the central power countries signed armistice agreements. World War 2 began in September 1939, when Chancellor Adolf Hitler, invaded Poland. Britain and France responded by declaring war on Germany. German treatment to people reflected Nazi ideas; concentration camps were gaining more power. The defeat on Germany happened in May 1945. World War 2 ended and the United States and the Soviet Union kept on being the two dominant powers of the world.
World War 2 caused the end of the European imperialism in the twentieth century. The main consequence that was brought by the European Colonialism was that Europe was no longer the arbiter of world affairs, as people didn't trust them anymore. Cold War was a long period of tensions between the democracies of the Western World and the communist countries of Easter Europe. Although the United States and the Soviet Union never officially declared war on each other, they indirectly fought. They wanted to demonstrate their technology and power. It came to an end in 1991 when the Soviet Union Collapsed. In 1990 Iraqi invaded Kuwait, after they tried to find an Arab solution, the USA decided to intervene in order to punish Saddam Hussein for his actions, and to show the world that this was not acceptable.