It would be a very different world.
The Hundred Years War and the Napoleonic Wars would never have happened. There would have been no War of the Roses, no Tudors, no Stuarts, no Hanoverians. It's unlikely that the English colonization of the New World would have taken place, or if it did...
What would have been the effect of the Klondike Gold Rush occurring in 1866, instead of 1896? Would Alaska have gone from distant white elephant to the jewel in the crown of the Russian Empire? How would this have affected Russian military priorities? If Russia began to assert itself as a...