Given his feats & how many men he single-handedly captured during his career, a strong case could be made for him having been history's greatest soldier.

Probably every movie with a battle scene where the two sides get involved in hand to hand combat. Doesn't it usually boil down to both the protagonist and antagonist for some reason being the best fighter in each army, slicing their way through hordes of nameless extras until they meet somewhere in the middle of the field for solo combat? Also once engaged in a fight with each other the extras seemigly become content to ignore them and let them have their solo duel.

I'm just happy to have stumbled across someplace to banter about antiquity with other like-minded history enthusiasts.

Julius Caesar's reputation for being magnanimous is somewhat overblown.

He could certainly be magnanimous when the enemies were fellow Romans, and there was a political benefit to be mined from it, but if the enemies were foreign and there was no political benefit from showing mercy, or he instead benefitted from being ruthless...he was ruthless.

There are plenty of examples of Caesar being brutal with his Gallic enemies. Avaricum for example, where a city of some 40,000 was put entirely to the sword, or the aftermath of Uxellodunum where Caesar ordered the hands of all the Gallic prisoners lopped off, before scattering those prisoners throughout Gaul, so they would be a demonstration of the price of raising one's sword against Rome. Going father back in his career, he also was quite ruthless in his retaliation against the pirates who had held him for ransom. Execution for pirates was not necessarily a given, as Pompey for example famously spared many of the Cilician pirates following his suppression of them, pardonining those who had turned to piracy out of desperation due to poverty, and resettled them in cities. In short the execution of Vercingetorix was not really out of character for Caesar.

It's impossible to say of course what motivated the decision not to show clemency, as his thoughts on the matter were never recorded. I do recall watching a BBC documentary about Alesia ages ago where one of the historians on the programme speculated that Caesar probably knew Vercingetorix personally prior to the rebellion, as Caesar frequently met with tribal leaders during his campaigns & Vercingetorix was an important figure among the Arverni, who were also one of Gaul's most powerful tribes. He posited that the reason for Vercingetorix's execution my have been personal rather than political - that Caesar was angered that Vercingetorix had pulled the wool over his eyes. Again though, that was just speculation.

They couldn't conquer Britain but they also couldn't lose. On it's own Britain had no means of returning to continental Europe.

Germany lost the war with it's Soviet misadventure.

It's not so much that the Norse learned French, it's that the Norse settlement in Normandy tended to be localized to certain places like Rouen, and on the whole did not displace the native Franks, who remained the majority. The Norse also intermarried with the native Franks almost immediately, so by the time you get to William the Conqueror's day the Norse had long since been absorbed by the Frankish majority. The Normans of William's day spoke a dialect of French, because their ancestors had also been Franks.

William the Conqueror didn't inspire Norman adventurers in the Mediterranean. They were present in the region long before William was born.

Normans had been fighting as mercenaries in the Mediterranean region both for Lombard counts and the Byzantine empire since the 900s. That was the origin as well for the branch of the Hauteville family that eventually ruled as Kings of Sicily. They had come to Italy as mercenaries / adventurers around 1035, only a few years after William the Conqueror's birth. Robert Guiscard became Duke of Apulia in 1059, six years prior to the Norman conquest of England.

The Normans had been busy carving out fiefdoms in southern Italy at the expense of the Lombards or Byzantines since William had been a child. The conquest of Sicily occured after William, but a Norman military presence had been a fact of life in southern Italy for many years prior, and they had already been carving out fiefdoms that were putting them on a trajectory for conflict over Sicily.

Side note, Robert Guiscard is the most interesting Norman warlord IMO, despite William having greater fame, and his wife Sikelgaita (although she was a Lombard, not Norman) was also a badass. She sometimes accompanied Robert on campaign, commanded at the siege of Trani, and brought reinforcements to Robert while was campaigning against the Byzantine empire. At the battle of Dyrrachium, while in full armor, she railled some of Roger's troops as they wavered following a Byzantine repulse. The Italian Normans were also playing in a far more interesting historical sandbox with a more diverse and interesting cast of characters. Byzantines! Lombard counts! The papacy! The emirate of Sicily! Plus Norman Sicily, at least early on, is fascinating in that it was one of the more tolerant medieval states & produced some interesting cultural exchange between the Normans, Greeks, and Muslims of southern Italy & Sicily.

The "Viking" link to the Normans however is quite often overstated.

It is certainly true enough that William was a direct descendant of Rollo, and that many Norse had come to settle in Normandy, but not all of these had been Vikings. Viking was a job rather than an ethnicity, and not every Scandinavian that came to Normandy did so as a Viking (sea raider / pirate). There were also merchants, fishermen, tradesmen, farmers, ect.

Second, the Norse settlement tended to be localized in certain places in Normandy like Rouen, and on the whole the native Franks of Normandy were not displaced and remained the majority. It was not too dissimilar to the later Norman conquest of England in that regard. Almost immediately there was also a great deal of interrmarriage between the Franks and the Norse, including with Rollo himself. By the time you get to 1066 that Norse minority had long since been absorbed by the Frankish majority, and the Normans spoke a dialect of French. The Normans in 1066, in short, were much more French than Norse. They also called themselves Franks.

Finally, most of the army William took with him to England wasn't even recruited in Normandy. Normans held the center of the field at Hastings but the left was composed of Bretons and the right men from other regions of France like Picardy or Boulogne, as well men as from Flanders.