55 BCE:

Julius Caesar attempts to invade Britain, but is met with strong resistance from the local tribes, who elect a super-leader: the Celtic King Eowyn, who summarily becomes the first member of the Britannian Imperial Family.

1603 CE:

Henry IX, the son of Elizabeth I, ascends to the throne after the death of his mother, starting the Golden Age of the Tudor Dynasty.

1776 CE:

American Colonies declare independence from the British Empire

1778 CE:

The Duke of Britannia bribes Benjamin Franklin with promises of titles and territories in the colonies. Franklin had been charged with appealing to Louis XVI for assistance in the American colonies' war for independence. Thereafter, he is given the title of Earl.

1781 CE:

The Continental Army suffers a decisive defeat during the Siege of Yorktown, marking the end of the American movement for independence.

1789 CE:

The western world enters the Age of Revolution, with numerous national revolutions taking place starting with France, except in the British Isles, under the rule of King Henry X, who continues to hold an absolute monarchy. This leads to the formation of the European Union.

1804 CE:

Napoleon Bonaparte rises to power in the European Union.

1805 CE:

European Union Navy engages the British Navy in a decisive victory at Trafalgar.

1806 CE:

EU forces invade Great Britain and occupies London.

1807 CE:

Queen Elizabeth III retreats to Edinburgh, where a revolutionary militia arrests her and forces her to abdicate, ending the monarchy. This becomes known as The Humiliation of Edinburgh. However, Sir Ricardo von Britannia, Duke of Britannia, and his friend and subordinate, Sir Richard Hector, Knight of One, bring Elizabeth III and her followers to the New World and establish a capital on the east coast of North America. The British Isles fall under the control of the EU and a new government is established.

1812 CE:

Elizabeth III nominates her lover, Sir Ricardo von Britannia, as her successor upon her death. She ends her reign for being "the Queen who loved throughout her stormy life". The Holy Britannian Empire is established with Ricardo von Britannia becoming the first Emperor of the new regime.

1945 CE:

The Quintipartite War between Holy Britannian Empire, European Union, Russian Federation, African Hegemony, and Chinese Federation begins with the invasion of Japan as part of Operation Swiftsure. Japan lasts only a month before surrendering, providing a buffer for Britannia to allow it full control of the Pacific. The war would wage for 18 years and claim nearly a quarter of the world's population with no discernible victor outside of the African Hegemony's destruction.

1960 CE:

Prince Arthur zi Britannia successfully launches a coup d'état of the Holy Britannian Empire, overthrowing Emperor Percival von Britannia and ending the von Britannia line. Using a mixture of swift ruthless strikes and realpolitik changes, his actions change the worldwide balance of power.

1963 CE:

The Quintipartite War officially ends with the Requiem Accords signed by the remaining four powers. As a result of the accord, the United Nations are founded.

1970 CE:

Lionel 1 lands on Luna. Alexander Armstrong becomes the first human to walk on Luna and the first human to walk on an astronomical object other than Earth.

2034 CE:

Armstrong Base is formally founded as the first human settlement on Luna, it is the first of six bases established by the various major nations over the next three years.

2052 CE:

Eldrin las Britannia rebels against the throne and is exiled along with his followers to Alpha Centauri.

2077 CE:

Liara T'Soni is born.

2099 CE:

The Holy Britannian Empire Space Agency establishes Bedegraine City in Eos Chasma and becomes the first permanent human settlement on Mars.

2132 CE:

The Eldfell-Ashford Energy Corporation demonstrates helium-3 fuel extraction from the atmosphere of Saturn.

2134 CE:

Steven Hackett is born.

2137 CE:

David Anderson is born

2140 CE:

Construction of Galerkin Station (Jump Zero) begins beyond the orbit of Pluto.

2143 CE:

Trace amounts of Element Zero are discovered on Mars.

2144 CE:

February 20th: Schneizel el Britannia is born

2145 CE:

January 13th: Cornelia li Britannia is born

2146 CE:

Thane Krios is born

Clovis la Britannia is born

2148 CE: Humanity Discovers Mass Effect Physics

Humanity discovers a small cache of highly advanced Prothean technology hidden deep beneath the surface of Mars on the south polar region of Promethei Planum. Building on the remnants of the long extinct race, human quickly explore the science of mass effect fields, leading to the development of faster than light travel and begin detailed exploration of the Sol System.

2149 CE:

Following information from the translated data cache on Mars, humans discover that Charon, Pluto's moon, is actually a massive piece of dormant Prothean technology, a mass relay, encased in ice. Once activated, Johnathan Grissom leads the first team of explorers through the relay, which instantaneously transports them to another relay in Arcturus, 36 light-years away. The explorers discover that the mass relays are part of a vast network, making travel across the galaxy possible.

The United Nations is dissolved with the signing of the Systems Alliance Confederation Charter spearheaded by the four major nations, and signed by every country on Earth. The Alliance soon becomes the military and exploratory spearhead of humanity.

With the discovery of the Mass Relay at Charon and the news that humanity may not be alone, the Holy Britannian Empire initiates Project Safehold, the search for a planet that may be outside of the Mass Effect relay system to hide humanity in the event of an extinction-level of event. No other nation is informed of this measure.

2150 CE:

Miranda Lawson is born

The Systems Alliance begins the first surveys for colonization prospects outside of the Sol System. One of these surveys discover the planet Terra Nova.

2151 CE:

To defend its expanding territory, humanity begins constructing a massive military fleet and space station at Arcturus, the nexus of several key mass relays, even though they have yet to encounter another intelligent spacefaring race.

An accident at the Singapore International Spaceport exposes hundreds of humans to dust-form Element Zero. Roughly 30% of the children born in Singapore after Element Zero exposure suffer from cancerous growths.

2152 CE:

The Toromo Agency, a major consortium based on Earth, begins settlement of humanity's first extra-solar colony world, the planet Demeter. Later that year, additional colonies are founded on Eden Prime and Terra Nova.

Thane Krios is submitted for training as an assassin under the Hanar.

June 14th: John Shepard is born.

2154 CE:

A containment failure at the newly constructed Londinium Station claims the lives of thirty-eight thousand Britannians.

Project Safehold is shut down. All resources, personnel, and funding attached to the project mysteriously disappears.

March 29th: Kallen Kōzuki is born

April 11th: Jane Shepherd is born.

July 10th: Suzaku Kururugi is born

December 5th: Lelouch vi Britannia is born.

2155 CE:

Saren Arterius is promoted to active service in the Turian military at the age of 16.

The Systems Alliance occupies completed portions of Arcturus Station, intended to become the Alliance's headquarters. Additional sectors are opened for the major nations military leaders.

Jeff "Joker" Moreau is born.

2156 CE:

Arcturus Station is formally inaugurated.

A small number of human children exposed to element zero exhibit minor telekinetic abilities.

Kai Leng is born.

2157 CE:

Pluto's orbit becomes circularized as a result of mass relay operations.

Jacob Taylor is born.

David Anderson graduates from Officer Candidate School with the rank of Second Lieutenant. He later that year graduates and receives the designation of N7.

2157 CE: The Humiliation
Humanity makes violent first contact with another spacefaring race: the Turians. The Turians observe human explorers attempting to activate a dormant mass relay, a practice forbidden by galactic law after the Rachni Wars, and attack. Over the next ten months, humanity finds itself on the losing side of what is forever known to humanity as The Humiliation and by the Turians as the Relay 314 War.

The Humiliation could have, at one point, been avoided during the events after the occupation of Shanxi, when the Citadel Council, now fully aware of the existence of a previously unknown race and the Turians beginning to prepare for full-scale war, interceded. However, all hope disappeared when the Turians discovered one of the espionage probes launched into Turian space and the demolition fusion warhead. With this evidence, the Turian Hierarchy demanded and received approval from the Citadel Council for the pacification of the Systems Alliance.

With the approval given, it was only a matter of time between the internal weakness of the Systems Alliance and the overwhelming might of the Turian Hierarchy that eventually Systems Alliance voted for surrender. However, even with the surrender, the Holy Britannian Empire, the Russian Federation, and Chinese Federation continued to resist, resulting in dreadful Turian losses as the fighting in the major cities continued.

It was only after the simultaneous assassinations of all three leaders, Emperor Charles zi Britannia, President Dmitri Probkharov, and Premier Hu Song-lin, by Spectres that the three powers surrendered to the Turian Hierarchy.

With the last bastions of resistance now defeated, the Turian Hierarchy, with the approval of the Citadel Council forces the Systems Alliance to sign the Erta Ale Accords, reducing Earth and its remaining existing colonial holdings into a "client state" of the Turian Hierarchy in order to "rehabilitate" humanity to be "responsible members of the galactic community".

Key sections of the Erta Ale Accords:

Article 227 charges the former leaders of the Systems Alliance, with "supreme offense[s] against intergalactic morality and the sanctity of treaties", and that Turian Hierarchy and Associated Powers would "request ... the people of the migrant fleet [to] surrender to them of the ex- leaders in order that they may be put on trial."

Article 231 (the so called "War Guilt Clause") stated humanity accepted responsibility for "all the loss and damage to which the Turian Hierarchy and Associated Governments and their nationals have been subjected as a consequence of the war imposed upon them by the aggression of Humanity"

Military restrictions: Humanity allowed a military that includes half the number of dreadnaughts and redraws the ration of the Treaty of Fairaxen to 10:6:6:2:1 where for every 10 dreadnaughts the Turian Hierarchy has humanity may possess 1.

Holy Britannian Empire institutes the After Humiliation calender with 2157 being the inaugural 0 AH

2158 CE (1 AH):
Former Imperial Consort Marianne vi Britannia is coronated as Empress of the Holy Britannian Empire.

Humans learn the potential of biotics. An international effort to track Element Zero exposure begins. Roughly 10% of recorded exposed children show indications of biotic ability.

2159 CE (2 AH):

Saren Arterius becomes the youngest Turian inducted into the Spectres.

The Systems Alliance is forced to purchase Galerkin Station back from the Turians for full cost and converts the facility into a biotic research and training facility.

2160 CE (3 AH):

The Systems Alliance Parliament is formed with Turian oversight.

With the existence of human biotics firmly established, the Biotic Acclimation and Temperance Training (BAaT) program is set up on Galerkin Station to train potential candidates and develop biotic implants.

The biotic drug red sand is first used.

The Blue Suns mercenary group is founded by Zaeed Massani and Vido Santiago in the Skyllian Verge.

Kasumi Goto is born.

2161 CE (4 AH):

Amid the insistence of the Turian Hegemony for worries over gene therapy and genetic medication making humanity uncontainable, the Systems Alliance Parliament is forced to pass the Sudham-Wolcott Genetic Heritage Act. This imposes sharp restrictions on all uses of genetic engineering, but provides subsidies for "approved" applications.

Tali'Zorah nar Rayya is born.

Jack is born.

Citing a "lack of faith" in the Systems Alliance, the Holy Britannian Empire withdraws from the Systems Alliance and opens up diplomatic and trade ties with the Quarian Migrant Fleet, Batarian Hegemony, various Krogan clans, and a majority of the Council races. The Systems Alliance suffers a massive loss of prestige and power and the Empire rapidly ascends in power to the consternation of the Turian Hierarchy.

Britannia reveals the 'K' Program, similar to the N7 Program, to the public and begins a massive military reorganization and buildup after leaving the Systems Alliance.