Introduction
Total War: Shogun 2 is a game of two halves: strategic play - such as recruitment, construction and the conquest of provinces - occurs on the campaign map; tactical play - individual battles fought in 3D against a real or AI opponent - occurs on the battlefield.
Attaining Victory in Shogun 2
In Shogun 2, the principle object of the single player campaign game (along with fulfilment of your victory conditions) is for your daimyo to become Shogun - the military ruler of all Japan. If your daimyo is to become shogun you must first defeat the current shogunate, the Ashikaga clan, capturing and holding the capital, Kyoto, for four seasons. At this point the Emperor will declare your daimyo Shogun.
Realm Divide
In Shogun 2 you can make a bid for the Shogunate at any time, although the current incumbent may pre-emptively attack you if you become too powerful and famous amongst the other clans. War with the Shogun for either reason will result in other clans declaring war on your own in support of the status quo; this stage is known as the "realm divide". This includes clans that were your staunch allies up to this point – after all, no-one likes a bully!
Being Shogun
In Shogun 2, once the Emperor has declared your daimyo Shogun, you will be awarded a unit of Shogun cavalry in Yamashiro province and the flagship "Nihon Maru" in the Eastern Seto Inland Sea. Additionally, your seasonal tax income will increase and your armed forces will receive a morale bonus.
Attaining Victory in Rise of the Samurai
The three great clans of the Gempei War are each split into two families. The principle object of the campaign game is to achieve hegemony over the other major families and minor lords, either through conquest or by spreading your family's influence throughout the provinces. Fame still gauges how powerful - and dangerous - your family is perceived as being within Japan, but there is no Shogunate to overthrow in order to achieve victory. If you become too powerful Emperor Go Shirakawa will declare you an enemy of the state, at which point all other families will move to attack you - including your "sister" family.
Attaining Victory (Fall of the Samurai)
The Boshin War is a conflict between the forces of the Shogunate and those of the Emperor. Every clan must pledge allegiance to one or the other. The principle object of the campaign game is to secure their allegiance to your cause and capture territory, including the capital city, Edo. Fame still gauges how powerful - and dangerous - your clan is perceived as being within Japan. When fame reaches a certain level you must choose to rally behind one power or the other, declaring war against all clans with allegiance to the opposition and fighting to defeat them. Alternatively, you can attempt to assume personal control of the country, which will lead to all but your most loyal allies turning against you.