Spying is practiced as long as we know the war. People from old times to newer times have been interested in knowing about their enemies before they attack on them from behind. Knowing your enemy’s strengths weaknesses can bring you an advantage over them, even if they are in large amount compared to your strength and number of troops.
During the crusade, Salahudin Ayyubi mastered spying and espionage. He smashed crusader armies and regained the city of Jerusalem or Bait Ul Muqaddas as known by Muslims. He is thought to be the first one who begin training commandos and elite forces which had supreme command over their specialties and were key units of Muslim army.
During cold war, both the Soviet Union and United States hired capable spies. They were mentally and physically tough people, who had trained for long. They were healthy people, had good habits of eating and sleeping, http://viamanreview.com/ provides all the information on improving your lifestyle. They were the people who really fought the cold war.
These days, states like Israel and India use their trained spies for terrorist attacks and assassinations of the leaders of Muslim countries they are against, especially Pakistan. As we know from our past, spying will continue as long as war. And it is not going to end till last day.