Samurai and Bushido
The decline of central power, aristocrats took it upon themselves to take justice. They turned to military force, causing a new army to form. This force were referred to as Samurai. Samurais were usually used only by wealthy people and were used to protect these people and their stuff. Their name even means, "those who serve."
Like knights, Samurai's have to follow a certain code. And this code is called Bushido. A Bushido translates out to, "the way of the warrior."
Samurais would help rich people protect things that are important to them. This had a great effect on the time, since they were all trained to do just as they were tasked. The only negative effect was that not everyone was able to have a samurai, only aristocrats could have one.
Bushido had a great effect, since it helped keep the samurais in check.
I'm a samurai in the 14th century. My duty is to protect and serve. I make sure that superiors don't get important items stolen by enemies. I always wanted to be a samurai, I always wanted to help others.