In 1592, and again in 1597, Toyotomi Hideyoshi, aiming to attack China ?,?,?, through Korea, mobilized an army of 160,000 peasants and samurai and deployed them to Korea. See Hideyoshi's invasions of Korea, Cho,sen seibatsu ?,?,?,?,?. Taking benefit of arquebus mastery and broad wartime experience from the Sengoku period, Japanese samurai armies made big gains in most of Korea. Kato, Kiyomasa advanced to Orangkai territory present day Manchuria bordering Korea to the northeast and crossed the border into Manchuria, but withdrew after retaliatory attacks from the Jurchens there, as it was clear he had outpaced the rest of the Japanese invasion force. some of the more famous samurai generals of this war were Kato, Kiyomasa, Konishi Yukinaga, and Shimazu Yoshihiro. Shimazu Yoshihiro led some 7,000 samurai and, in spite of being heavily outnumbered, defeated a host of allied Ming and Korean forces at the fight of Sacheon in 1598, near the conclusion of the campaigns. Yoshihiro has been feared as Oni Shimazu "Shimazu ogre" and his nickname spread across not only Korea but to Ming Dynasty China. In spite of the superiority of Japanese land forces, finally the two expeditions failed although they did devastate the Korean landmass from factors like Korean naval superiority which, led by Admiral Yi Sun sin, harassed Japanese supply lines continuously during the wars, ensuing in supply shortages on land, the commitment of sizeable Ming forces to Korea, Korean guerrilla actions, the underestimation of resistance by Japanese commanders in the 1st campaign of 1592, Korean defenses on land were caught unprepared, under trained, and under armed, they were quickly overrun, with only a restricted number of effectively tolerant engagements against the more experienced and battle hardened Japanese forces in the second campaign of 1597, Korean and Ming forces proved to be a far more hard challenge and, with the backing of continued Korean naval superiority, restricted Japanese gains to parts southeastern Korea, and wavering Japanese commitment to the campaigns as the wars dragged on. The last death blow to the Japanese campaigns in Korea came with Hideyoshi's death in late 1598 and the recall of all Japanese forces in Korea by the Council of Five Elders established by Hideyoshi to supervise the transition from his regency to that of his son Hideyori.
Many samurai forces that were active during this period weren't deployed to Korea, most importantly, the daimyo,s Tokugawa Ieyasu carefully kept forces under his command out of the Korean campaigns, and other samurai commanders who were opposed to Hideyoshi's domination of Japan either mulled Hideyoshi's call to attack Korea or contributed a small token force. Most commanders who did opposed or otherwise resisted or resented Hideyoshi ended up as part of the so called Eastern Army, while commanders loyal to Hideyoshi and his son a notable exemption to this trend was Kato, Kiyomasa, who deployed with Tokugawa and the Eastern Army were mainly dedicated to the Western Army, the two opposing sides so named for the relative geographical places of their respective commanders' domains could afterward clash, most notably at the fight of Sekigahara, which was won by Tokugawa Ieyasu and the Eastern Forces, paving the way for the establishment of the Tokugawa Shogunate.
Social mobility was high, as the ancient regime collapsed and rising samurai required to maintain big military and administrative organizations in their regions of influence. Most of the samurai families that survived to the 19th century originated in this era, declaring themselves to be the blood of one of the four ancient noble clans: Minamoto, Taira, Fujiwara and Tachibana. usually, but, it's hard to prove these claims.
Oda Nobunaga was the well known lord of the Nagoya area once called Owari Province and an exceptional example of a samurai of the Sengoku period. He came inside some years of, and laid down the path for his successors to follow, the reunification of Japan under a new Bakufu Shogunate.
Oda Nobunaga made innovations in the fields of organization and war plans, heavily used arquebuses, worked on commerce and business and treasured novelty. Consecutive victories enabled him to realize the termination of the Ashikaga Bakufu and the disarmament of the military powers of the Buddhist monks, which had inflamed futile struggles among the populace for centuries. Attacking from the "sanctuary" of Buddhist temples, they were constant headaches to any warlord and the Emperor who tried to control their actions. He died in 1582 when one of his generals, Akechi Mitsuhide, turned upon him with his army.
Importantly, Toyotomi Hideyoshi see below and Tokugawa Ieyasu, who founded the Tokugawa Shogunate, were loyal followers of Nobunaga. Hideyoshi began as a peasant and became one of Nobunaga's top generals, and Ieyasu had shared his childhood with Nobunaga. Hideyoshi defeated Mitsuhide inside a month, and has been regarded as the rightful replacement of Nobunaga by avenging the treachery of Mitsuhide.
These two were able to use Nobunaga's last accomplishments on which build a unified Japan and there was a saying: "The reunification is a rice cake, Oda made it. Hashiba shaped it. At last, only Ieyasu tastes it." Hashiba is the family name that Toyotomi Hideyoshi used while he was a fan of Nobunaga.
Toyotomi Hideyoshi, who became a great minister in 1586, himself the son of a poor peasant family, produced a law that the samurai caste became codified as permanent and inherited, and that non samurai were forbidden to carry weapons, thus ending the social mobility of Japan up till that point, which lasted till the dissolution of the Edo Shogunate by the Meiji revolutionaries.
it's important be aware of that the differentiation between samurai and non samurai was so obscure that throughout the 16th century, most male adults in any social class small farmers belonged to at least one military organization of their own and served in wars before and throughout Hideyoshi's rule. It may be said that an "all against all" situation continued for a century.
The authorized samurai families after the 17th century were those that chose to follow Nobunaga, Hideyoshi and Ieyasu. big battles occurred throughout the change between regimes, and some defeated samurai were destroyed, went ro,nin or were absorbed into the general populace.