Hmm.. Maybe:
Grand Campaign (1835-1920)
Why: This would be the entire time period of the game, and so it should definitely be included.
I can't think of good name right now... (1850-1920)
Why: This would start near the Crimean War (1853-1856), the arrival of Commodore Perry to Japan (1853), and other wars near this time, perhaps also this one could include the American Civil War as well?

(It is only within 10 years later that it started)
Can't think of one here either.. Maybe "Colonialism and War"

(1880-1920)
Or perhaps this should be an 1870 scenario, and then a 1890 or around that could be made also.
And then last, but not least, 1914-1920, which could be called "The Great War"
Meiji-Tenno
PS: I have seen some people have asked about Russo-Japanese War's dates. The fighting started at Port Arthur on February 8,1904, and ended on September 5, 1905 when the treaty of Portsmouth was signed, at the city of Portsmouth, in the state of New Hampshire of the United States.