[Cal-Reflector]

My Japanese is proficient, but not perfect (say 85%). I'll identify places I don't get/am murky on and late coming experts can just fill in those spots:

大航海時代のきっかけとなったのは、当時ヨーロッパで進んでいた、錬金術に端を発した、
ストーン・ヘンジ周辺などから発見された賢者の石＝サクラダイトを動力源とするための研究。
サクラダイトは絶対量が少なく、研究の発展が妨げられていたが、
マルコ・ポーロの「世界の記述」にある黄金の国ジパングに大量に存在すると考えられた。

At the advent of the Age of Discovery, Alchemy was moving forward in Europe, driven by the research around the Philsopher's Stone (Sakuradite) to turn it into a source of energy; sakuradite was first discovered near the Stone Henges. The scarcity of sakuradite impeded the research's progress, however, in "The Million" (The Travels of Marco Polo), Marco Polo mentions the land of gold, Japan, where sakuradite existed in abundance.

（16世紀位）独身を貫いたエリザベス１世には息子、ヘンリー9世がおり、
父親候補はレスター伯・エセックス伯・ブリタニア公カールなどが有力とされている

In the 16th century, Elizabeth the 1st who remained single throughout her life had a son, Henry the 9th. The potential fathers--Robert Dudley, 1st Earl of Leicester, Robert Devereux, Earl of Essex, and Duke of Britannia Carl--gain influence and power as a result. (Thus, the Tudors do not end with the Virgin Queen; aside from Duke of Brittania Carl, the other two are real historical figures)

皇暦1770年代、アメリカでワシントンの乱勃発
当時のブリタニア公は、ルイ16世に独立支援を請うてフランスに渡った
ベンジャミン・フランクリンに、爵位と植民地アメリカの領地をちらつかせて買収（その後、伯爵となった模様 ）。
大陸軍はヨークタウンで大敗北を喫し、ジョージ・ワシントンが死亡。

Imperial Calendar, in the 1770s, the Rebellion of Washington takes place in America. The Duke of Brittania at the time bribes Benjamin Franklin with promises of titles and territories in the colonies, who was charged with appealing to Louis XVI for France's assistance in the colonies' war for independence. Thereafter, Benjamin Franklin seems to have become an earl. As a result, the Continental Army suffers a decisive defeat at Yorktown, George Washington dies.

皇暦1700年代の末、市民革命時代に入り、フランス革命を経てナポレオンが登場。
トラファルガー海戦に勝利し、ロンドンへ進軍。1807年、女王エリザベス3世はエディンバラに追い込まれ 、
革命派の市民軍に捕縛され王政廃止宣言を迫られる（エディンバラの屈辱）が、
ブリタニア公リカルド・ヴァン・ブリタニアと、その親友であり部下でもあるナイト・オブ・ワン の
リシャール・エクトル卿によって新大陸へと落ち延びた。

Towards the end of the 18th century, the Western world enters the Age of Revolution, after the French revolutions Napoleon emerges. He wins the Battle of Trafalgar and occupies London. In 1807, Queen Elizabeth the 3rd is chased to Edinburgh. where revolutionary militias arrest her and force her to abdicate and end the monarchy (The Shame of Edinburgh). However, The Duke of Brittania Ricardo von Brittania and his friend and subordinate Knight of One, Sir Richard Hector, sustains the Monarchy in the New World.

皇暦1813年、新大陸に渡ったテューダー朝の血筋が途絶え、
リカルド・ヴァン・ブリタニア1世が即位。ブリタニア年代記が作成され、カエサルのブリテン島 遠征を退け、
部族を独立させたとされるアルウィン1世の即位を元年とした皇暦を制定（皇暦元年時のローマ皇帝はアウグス トクス

Imperial Calendar 1813: The Blood of the Tudors who traveled to the New World comes to an end. Ricardo von Brittania the first ascends to the throne. The Brittanian year is established, with the origin year set as to the ascendancy of the first Celtic King Alwyn (Eowyn?) the First, from the tribes who defeated Caesar's invasion. At the time of Holy Brittanian Calendar's origin year, the Roman Emperor was Augustus, Caesar's successor.

Significant Conclusions:
1. Sakuradite was a driver of alchemy, so from the beginning people recognized the value of the mineral. It'd be a while until the age of science and super conductivity arrived however so I can't see people fighting wars over the substance until well after the industrial age and WWII. The discovery of sakuradite in Japan was a very modern event as well.

2. Benjamin Frankling turns traitor, never delivers the appeal to France, and as a result Britan wins the war over the American colonies. Fascinating.

3. Napoleon did exist (we can assume then, with all the historical figures already present, that most historical figures in the world of Geass would've remained extant), he did win Trafalgar, he did invade England, and succeed in gaining London. The mention of a revolutionary faction implies the existence of a royalist faction, who was probably overpowered by Napoleon's army aiding the revolutionaries. However, considering that Napoleon later crowned himself emperor and disillusioned many people (like Beethoven), the conflict in the British Isles may well have continued.

4. Seems like Ricardo disposed of the Tudors and made himself Emperor. Also surprisingly was the fact that at this point in time, America could not have been all that powerful in population, development, resources, and economy, especially after they lost the British Isles. Which meant that in roughly two centuries Brittania kept whatever territories/colonies/commonwealths from before, gained new ones, and came to prominence that we see them in today.