Short answers, pulled from the story.
The Romans planted the first vineyards in the Champagne region of northeast France by the 5th century. Emperor Domitian later issued an edict requiring all colonial vines to be uprooted, which slowed cultivation for decades.
Christopher Merret documented the addition of sugar to a finished wine to create a second fermentation six years before Dom Pérignon set foot in the Abbey of Hautvillers. Merret presented a paper at the Royal Society in 1662 detailing what is now called méthode traditionnelle.
True champagne must be produced in the Champagne region and made from the Pinot Meunier, Pinot Noir, or Chardonnay grapes grown in this region. The name is legally protected by European law and an 1891 treaty.
According to the appellation d'origine contrôlée a minimum of fifteen months is required to completely develop all the flavour. For exceptional harvest years declared as millésime, the champagne must mature for at least three years.
Pinot noir and Pinot meunier are predominantly grown in two areas, the Montagne de Reims and the Vallée de la Marne. The Montagne de Reims run east to west south of Reims, while the Vallée de la Marne contains south-facing chalky slopes.
The trend towards drier champagne began when Perrier-Jouët decided not to sweeten his 1846 vintage before exporting it to London. The designation Brut Champagne was created by Pommery for the British in 1876.