I started in 1011 as a dwindling Lotharingia, a weak prince in the greater HRE surrounded by a growing France to the south and a dominant Saxony in the east. Luckily I was able to ally both of them, and swiftly united the Dutch with a war against Holland, Frisia and Flanders. 

I spent the next 50 years developing and building the nation to ready it for two main wars: against England to gain a foothold on the British Isles, and against a weaker neighboring Elector (The Palatinate) of the HRE to usurp their title. 

I managed to diplo-vassalize the many small states in Flanders, Rhenia, Elsaß and Lorraine (per the map), and I subjugated a weak and feeble Burgundy that had been pushed back into Arpitania. This move incurred the wrath of the French who managed to gain a personal union over a MASSIVE Byzantium, but was struggling with loyalty. 

Around this time I gained a PU over Hungary as the king died without an heir through our royal marriage, and I secured alliances with the other major HRE states and Poland. After finishing off England I helped Byzantium out of their PU with an independence war, and rallied my allies against the French (who by now have also united Iberia in a Reconquista, so they were formidable!).

I used this opportunity to retake all of Burgundy's cores, release Champagne as a vassal, and finish uniting the disparate Walloons under one duchy. Burgundy was swiftly integrated, and thus the borders on the map were established.

The new royal situation of Byzantium was shaky as no one could agree who should assume the mantle, but eventually one king proclaimed himself ruler. We entered a royal marriage, and he then died "mysteriously" without an heir, bringing the massive and newly freed Empire of the East under the fold of Lothaire. They were surprisingly loyal thanks to the relations and trust we built with them in decades prior!

EU4 Extended Timeline: A resurgent Lotharingia conquers England after William of Normandy fails!