Speaking of military might, these guys were a force to be reckoned with. Things didn't end so good for them though.
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The standing Ottoman army, first organized by bey (also erroneously called sultan) Murad 1 in the late 14th century, lasting until 1826, altogether about 450 years.
The term in Turkish, yeniçeri means new troops, indicating exactly what they were in the beginning: An alternative to the old regular army.
The Janissaries became famous for their military skills, but also because they were staffed by youths conscripted from Christian families in the Balkans. After the conscription they were defined as the property of the sultan, and practically all of them converted to Islam.
The Janissaries were subject to strict rules, limiting their freedom and demanding higher moral standards than usual in the society. In the first couple of centuries, they were forced to celibacy, but this would later change. The janissaries were not allowed to grow beard, which was the sign of a free man.
The need for the bey/sultan to form the Janissary corps, came from the fragility of an army put together by free men from many different tribes from areas often wide apart. Their allegiance were normally to their own tribal leaders, leaders that often were tempted to oppose the power of the sultan, and to find allies among the main enemies of the Ottoman empire.
At first the Janissaries were put together of war prisoners. But from 1420's young men were taken from their homes at an early age, and contact with their old communities were cut. This system was called devsirme. They were even denied contact with the normal society in the areas were they were stationed. Through their training, they were learned to put their allegiance to the bey/sultan. At least so was the intention. And despite strict rules, they enjoyed high living standards and a social status which intended to give logic and force to their loyalty.
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