The British are a people hailing from the British Isles in Northern Europe. In the New World they were one of the most powerful colonists defeating multiple European powers there. They eventually established thirteen colonies, which later revolted against the Britain Empire to form the United States of America. They controlled Canada until 1867 and still have major influence there today.
The British in Age of Empires III can obtain a powerful economy because they can create Settlers faster than other civilizations. Early in the game it is best to focus on gathering Wood for the Manor Houses so more settlers will be spawned.
The British military is very powerful especially later on in the game because Musketeers and Hussars, two mainline and versatile units, can later on become upgraded to a Royal Guard level. The British Home City is also very useful because it focuses on its technology and the navy.
The units speak a variant of Middle English. In the campaign scenarios, the Americans speak modern English. The pronunciation of the Middle English used in the game ranges from something very phonetic (as it's written) to something closer to the more abstract pronunciation of Modern English. Different units also show different dialects, for example hot air balloons say "ish" instead of "ee" when saying "I", and sometimes "th"s are pronounced as "d"s, and short e/a/uh sounds are in words that are no longer in Modern English. Sometimes the pronunciation even sounds like a tradition Scots accent, if not a bit more archaic.
Question marks (?) have been added where there is only a vague definition or translation or even less, and brackets immediately after the in-game dialogue sample give a rough pronunciation.
I meane so (ee/ish mehne soh) - I mean so
I woll (ee/ish woll) - I will
commandement - what is it/your command? (commandment)