Final answer:
Oda Nobunaga was the leader whose efforts helped end the 'warring states' period in Japan, which was later unified under the rule of Tokugawa Ieyasu with the establishment of the Tokugawa Shogunate.
Step-by-step explanation:
The leader whose rule ended the 'warring states' period, even though he did not succeed in unifying Japan, was Oda Nobunaga. Oda Nobunaga was one of the powerful samurai known as "the three unifiers" who began to unite Japan under his rule in the 1560s. He initiated the process that would eventually lead to the end of the incessant violence and the uniting of Japan under a strong central government. Following Oda Nobunaga's death, his vassal Toyotomi Hideyoshi continued his efforts and by 1590 had brought all the daimyos into submission. However, it was Tokugawa Ieyasu who ultimately secured a decisive victory at the Battle of Sekigahara and established the Tokugawa Shogunate, ushering in the Edo period, which brought peace and stability to the country.