What are Ninja and Ninjutsu?

A person who uses Ninjutsu is a ninja. Ninjutsu is not a martial art. Ninjutsu is an independent art of warfare that developed mainly in the regions of Iga in Mie Prefecture, and Koka in Shiga Prefecture, Japan.
So, do you know what kind of job ninja were doing?
Most people imagine that ninjas flew through the sky and disappeared, like Superman, waving ninja swords around, sneaking into the enemy ranks and assassinating generals… This is a mistaken image of the ninja introduced by movies and comic books.
The jobs of a ninja are divided into the two main categories of performing espionage and strategy. The methodology for performing espionage and strategy is Ninjutsu. Espionage is similar to the job of modern spies, wherein one carefully gathers intelligence about the enemy and analyzes its military strength.
Strategic activities are skills that reduce the enemy’s military power. Ninja did not fight strong enemies by themselves. Ninja fought enemies after they had reduced the enemies’ military power. In times of peace, Ninjutsu was called an art of “entering from afar”, while in times of war, Ninjutsu was called an art of “entering from “nearby”, wherein ninja would constantly gather intelligence concerning the enemy, thinking of ways to beat the enemy, but not fighting the enemy directly. Ninja who thought rationally thought of war by intellect as great, and war by military strength (weapons) as foolish. Therefore, ninja who swing their ninja swords about can be called the lowest of the ninja.
The Ninjutsu of Iga-ryu and Koga-ryu stem from the same source, and are said to be the highest of the Ninjutsu.