Total War: Shogun 2 Expansion Announced

SEGA today announced Total War: Shogun 2 is getting a standalone expansion early next year.
Dubbed "Fall of the Samurai," the expansion includes 39 new units, new weapons, ten new ship types, three new agent types on the campaign map to choose from, four new historical scenarios, and brand new siege-battle mechanics.

Here is the description of the expansion story:

It is 1863, and the age of the Samurai is coming to a close. The masters of sword, bow and horse face a period of massive change as a new Japan is born to the bellowing of cannon and the shriek of steam engines. The modern Victorian world of Europe and America is battering at Japan’s gates, bringing revolutionary new weapons to the country; weapons which will sound the death-knell of the Samurai class.
This new world can be shut out and tradition upheld, or it can be embraced and mastered. Into this upheaval, a new, Imperial movement rises up against the old Shoguns, attempting to restore the Emperor as rightful master of Japan. Will you
back this rising Imperial power, or the Shogunate of old? Choose your path, and carry the country with you in the final battle for Japan’s future: the Boshin War, the War of the Year of the Dragon.
Fall of the Samurai hits in March 2012. No pricing details were revealed. Below is the trailer and some screenshots for the expansion.