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.
But over time, the Janissaries were so successful that they grew into one of the strongest power institutions in the empire. They could exercise this strength to influence the policy and to defend their own interests. From the 17th century and on, they staged many palace coups to exercise this power. But this would eventually be the main reason for their downfall — their strength made them dangerous to the sultan, and when the final battle over power came, the Janissaries lost, and all troops were killed or banished.
Other reasons for the sultan to want to remove the Janissaries were that they had grown into a large number, up from 20,000 in 1574 to 135,000 in their last year of 1826. This was expensive, and in addition the Janissaries had found their own (unacceptable) way of financing their military activities as well as their high living standard: they performed various trades and were more an more in contact with the society. They were truly a state in the state.
1380’s: Bey Murad 1 forms the first devsirme system, from which the Janissary army could be formed.
15th century: The Janissaries grow into becoming a powerful political force within the Ottoman state.
16th century: It has become standard for Janissary troops to marry, and they even manage to get the privilege that their sons should be allowed to enter their army, even if these were born Muslims.
17th century: More and more, the Janissary troops engage in palace coups. This would continue right onto their end.
1648: Janissary troops discharge and kills sultan Ibrahim 1.
17th century: The traditional devsirme system of conscription is abandoned, and they had many free men applying, among them many from Muslim families too.
1820’s: The Janissaries fails to crush the Greek fight for independence. By this, they proved that they were no longer the near-infallible army as they had been before.
1826 June: The Janissary corps find out that Sultan Mahmud 2 is forming new European-style armies, and revolts. The sultan declares war on them, and it ends with cannons shooting at the Janissary barracks in Constantinople and the provincial capitals, killing most of the troops. Many of the survivors were executed, others were banished. This ended the period of the Janissaries.