Hundred Years War
Historically, the Hundred Years War was a long conflict between England and France caused by inheritances of French territories by the English royal family, and the resulting dispute over which Kingdom those territories belonged to. (According to feudal law, they should have remained part of France, but since they had been inherited by the King of England, he had de facto control of them.) Historically the war ended in 1453, with England having lost all Continental territory except for Calais (and thus a clear, but not total, French victory).
In EU2's Grand Campaign (the 1419 scenario), the Hundred Years War is represented by a war in progress at game-start, with England, Burgundy and Brittany on one side, their opponents being France, Scotland, and various French vassal states. The outcome of this war often determines the relative strengths of England and France for the remainder of the scenario.
A player-controlled England's goal (assuming a strategy that involves partial or total conquest of France) should be the conquest of France, but more immediately Picardie province; an event can trigger beginning in 1453 that will remove French as a state culture if you do not control Gascogne, Poitou, Normandie, Caux, Picardie, and Calais provinces. A conquest-oriented England will of course wish to avoid this at all costs. See the discussion of the Hundred Years War in the strategy guide for England (2).
If England wishes to be uninvolved in Continental affairs, the easiest thing to do is to divert all forces to Scotland and force vassalize it (which will bring it into your sphere of influence rather than France's), then make peace with France offering all Continental territories.
France's goal, of course, is to recover all English territories on the mainland. (Players interested in playing France in the 1419 scenario are advised to consult Sheridan's France 1419 strategy guide.)