As England in MEIOU I started the game at war with France, being dragged in by my vassal Montfort. The war started terribly, my armies were scattered and were defeated in short order, it only until King Edward III Plantagenet himself brought an army of 30,000 from England to our southern territories and crushed Jean there, England fought alone with her vassals and allies, Montfort and Navarra in which the war was oddly lost in the north but won in the south and for all intent and purposes was a draw, but for some reason, even when I wanted to throw in the towel my vassal (who is leader in this war against Alancon, and even France herself is not able to sue for peace either) simply refused, kept fighting on despite being nearly overrun. It was the timely arrival of a 15,000 troop army that finally saved Montfort and tipped the balance of power to my side, but the war was still far from decided.
We fought for another year... making it 19 years the kingdoms and families of Plantagenet and Valois were at odds, before the Valois and French forces were delivered a final crushing blow that ended up being devastating for France. Aragon joined and brought Portugal and her Italian allies into the war. The remaining war was simply mop up operations as my armies chased small bands of French warriors around the country. For all intents and purposes the war was over... but still my vassal Montfort still refused to go to the negotiating table and get what they wanted and no doubt not be refused, but no, they continued the war, so I moved most of my forces north to invade Scotland... it was then I discovered Portugal just began invading it as well, so I quickly got my armies to the remaining territories and besieged them first.
When half of Scotland fell I got a message I never got before in any EU3 game or its mods.... 'the Valois (France's ruling family) recognized the Plantagenets (England's ruling family) as the victorious family and pledged Dauphine (which I assume is their province of birth) as English vassals which basically made what was left of France my vassal.
Now I get confused, apparently I am now fighting my vassals as there were no peace signed despite the message saying White Peace has been agreed upon between France and England. Does this also mean I should declare war on Aragon to protect my new vassals? I have the armies to defeat both Aragon and her pesky Italian allies. My manpower though is another matter completely, I nearly ran out halfway into the French war which caused me to pray that Montfort would sue for peace, but then my manpower returned and my armies were resupplied. I also believe it will be bit more difficult against Aragon but I plan to fight defensively, which will conserve my manpower.
Another thing I am also proud of is this is my first English game in which I never needed to mint to support my large army. Though my navy is an embarrassment, only 1 galley and 17 transports. I am already beginning construction of a large navy.