Espionage means obtaining secret information, without permission from the person who detains it information, through clandestine means. Espionage has been documented, all along human history, since ancient times. At the beginning, espionage was motivated solely by military or political reasons. In the modern era, when finances are such an important factor in obtaining and preserving political and military power, industrial and economic espionage has become common practice.
Throughout the history, people have used espionage to defend themselves, conquer others or simply for individual purposes, determined by greed or revenge. The methods of deception, diversion and subversion were pretty sophisticated, since the earliest times. They have also been documented and passed over to students, in all the ancient civilizations: Egypt, China, India, Greece and the Roman Empire. The Bible also mentions espionage incidents. The Mongolians also owe their conquests in Asia and Europe, mostly to espionage.
In the medieval times, espionage has been used successfully, by powerful nations and monarchs. Intelligence was gathered in Japan by the ninjas. In England, Elizabeth, used espionage frequently, to attain her purposes. Though, the most ruthless royalty figure and exceptionally skilled, in espionage was Catherine De Medici who had no scruple to use it, together with assassination, even against her own son.
During the modern times, espionage escalated to the level of war of intelligence. The Cold War between the Unites States of America and U.S.S.R. also involved their allies and its purpose was mainly, related to the possession of nuclear weapons. The competition between USA and U.S.S.R., for getting further and further away from Earth, into space, made actually part of The Cold War. At a certain point, both nations realized the advantages of spying on each other, on large geographical areas, through satellites.
These days, with different methods and forms of organizations, from country to country, espionage extends to law enforcement. Due to new historical circumstances, professionally trained agents are targeting illegal and terrorist activities, including drug and human trafficking.