It is true that King Bela sent bloody swords throughout his kingdom to raise the people. There is a record of Batu's missive to the king, demanding that the Russian Cumans and their leader Koten be handed over. Batu's message was stark and simple: 'Word has come to me that you have taken the Cumans, our servants, under your protection. Cease harbouring them, or you will make of me an enemy because of them. They, who have no houses and dwell in tents, will find it easy to escape. But you who dwell in houses within towns – how can you escape me?'

It is interesting to note that the demand was sent in Batu's name. As a senior prince and son to Jochi, the first-born of Genghis, he was in nominal command of the Golden Horde, as they were known. Yet it was Tsubodai who led them strategically and tactically. It was a complex relationship and it came to a head when news of Ogedai's death finally reached them. Budapest is around four and a half thousand miles west of Karakorum in the same land mass. Tsubodai's extraordinary campaign took the Mongol tumans right across Kazakhstan, Russia to Moscow and Kiev, Romania, Hungary, Poland, Lithuania, Eastern Prussia and Croatia. They were knocking on the door of Austria when Ogedai died. It was in fact the French King Louis IX who fixed a confusing name for the Mongols in European minds. As he prepared his armies to march, he told his wife that his soldiers would send the Tartars to hell, or the Tartars would send them to heaven. He deliberately punned on the Latin word for hell, 'Tartarus', and the erroneous name 'Tartar' stuck for centuries as a result.

I have omitted a detailed description of the battle of Liegnitz, which took place as the climax of Baidur's sweep through Poland. It is the nature of such a sweep that there are many battles, against varied opponents, but there is a limit to how many can be squeezed into a novel, even one about the Mongols. In history, Liegnitz is one of the few really well-known Mongol battles – omitting it is the equivalent of writing about Nelson without mentioning the Nile. For the sake of the plot flow, however, I think it was the right decision. At Liegnitz, Baidur used the feigned retreat, but he added the innovation of tar barrels that sent white smoke across the battlefield. This simple device prevented one half of a Polish army seeing what was happening to the other half. It could easily have been the climax of this book, but the other well-known battle is Sajo river and that was Tsubodai's triumph.

Tsubodai's final recorded battle combined not only a night attack and flanking manoeuvre, not only the masterful use of terrain in the way he made the river work for him, but also the now ancient trick of leaving a path for the enemy to escape, only to fall on him as he does. Tsubodai led three tumans across a ford to the south of the encamped Hungarian armies, sending Batu against the left flank at dawn, while the rest galloped further to hit the Hungarian rear. King Bela was forced to take refuge in his night camp, while the Mongols caused chaos with firecrackers, burning tar in barrels and shooting random arrows. They had gone from the prey to the hunter and made the most of it.

In the midst of the chaos, King Bela's men saw a ridge of ground running west that lay out of sight of the Mongols. He tested the escape route by sending out a small number, watching as they rode to safety. As the day wore on, the king tried to send his entire army from the camp. In their panic, they lost formation and were strung out over miles. It was at that point that Tsubodai's men attacked the column. He had scouted the ground. He knew the ridge and had deliberately left the route open to trap them. Depending on the source, the Mongol tumans slaughtered 40-65,000 of the Hungarian army, ending it as an entity for a generation or more. King Bela escaped the slaughter and fled to Austria. When the Mongols left, he went on to rebuild Hungary from ruins. He is still honoured as one of Hungary's great kings, despite his disastrous encounter with Tsubodai.

In many ways, it was a fitting end to Tsubodai's military career, though of course he did not see it like that. Hungary was in ruins when the news came of Ogedai's death and everything changed.

The brilliant tactical manoeuvres of Liegnitz and the Sajo river were rendered void by the Mongol withdrawal. They are rarely taught outside military schools, in part because they did not lead on to conquest. Politics intruded on Tsubodai's ambitions. If it had not, all history would have changed. There are not many moments in history when the death of a single man changed the entire world. Ogedai's death was one such moment. If he had lived, there would have been no Elizabethan age, no British Empire, no Renaissance, perhaps no Industrial Revolution. In such circumstances, this book could very well have been written in Mongolian or Chinese.