Japan
is unique among the worlds major countries as being one who fought
almost all of its battles on it's own soil. No other nations have such
a long history of civil strife where group after group take power only
to be toppled in turn. The Momoyama period being one of the bigger
periods of civil war. Having too many factions battling at this point I
will only breifly outline the key players.
Oda Nobunaga acheived control over the province of Owari (near Nagoya) in 1559. Along with most of the Daimyo he wished that Japan could be united. Being in this strategic location he suceeded in capturing the capital in 1568.
After establishing himself in Kyoto he slowly elliminated his enemies. Some of his biggest enemies were not Daimyo but militant Buddhist sects such as the pure land sect. Nounaga destroyed their monastary (Enryakuji near Kyoto) in 1571 and continued fighting them until 1580.
Nobunaga was fortunate with his two rivals to the east. Both Takeda Shingen and Uyesugi Kenshin died before they were able to confront Nobunaga. In 1575 he defeated the Takeda clan in the battle of Nagashino.
In 1582, general Akechi murdered Nobunaga and cuptured his Azuchi castle. Toyotomi Hideyoshi, a general fighting for Nobunaga quickly reacted defeating Akechi and taking control of what was Nobunaga's old army and holdings.
He continued to elliminate the remaining rivals. In 1583 he subdued the northern provinces and kyushu in 1587. After defeating the Hojo family in Odawara in 1590, Japan was finaly reunited.(2)
In 1600 a muddy, bloody battle Tokugawa Ieyasu(once Hideyoshi's ally) beat Hideyoshi and Japan once again gained a Shogun.
This was not the end as Hideyoshi's son along with 60000 disgruntled samurai shut himself up in Osaka Castle. What followed was a colossal seige where Tokugawa tried every trick from bribery to bombardment. The castle fell in 1615 outside the castle walls in the last ever large scale samurai battle.