The joke Mother Nature almost played on Human History
OK, so you guys know about the British Empire right? It's a beast that came about thanks to Brits and their little ships sailing and conquering places all over the world. One of the early expeditions gave us the USA, and later expeditions gave us all of these countries:

This is all thanks in part because Britain is situated on an island and therefore they were pretty much impregnable throughout history. Of course they did suffer some numerous invasions in the past (by The Vikings, Anglo-Saxons, and the Normans) but in the end, the invaders were only successful in invading half of Britain, which is England and even then, they got assimilated. Scotland remained independent till 1707 mostly because England and Scotland had had a same monarch for quite some time at that point.
Some parts of British history also saw Britain fighting with continental powers. The Hundred Years War, The Napoleonic Wars, and the two World Wars were instances where Britain launched offensives on the continent. In World War II, Hitler had a plan to invade Britain called the 'Operation Sea Lion' which was ultimately unsuccessful.
So, what is with all of these British history? Well...

Yup
This picture isn't just a horribly photoshopped image by a disgruntled Hitler who couldn't seem to get Britain off his back. This is a picture of Doggerland, a huge sunken landmass in the North Sea. This landmass was believed to have been dry land from around 18,000 BC until as late as 5,500 BC. One hypothesis said that it sunk thanks to a tsunami caused by the Storegga Slides which are underwater landslides.
Excavations from the area also revealed that humans and neanderthals have lived in the area. Here you can see photos of how Doggerlanders might've lived.
So, going back to British history here. Could you imagine what would've happened to Britain if Doggerland hadn't sunk? Do you think the British Empire would've happened if Britain had to deal with invasions all the time? Or, would Britain even exist at all?
What if, by some freak natural event, Doggerland had arisen during WWII? Would the Germans have won? Or at least maybe Britain would be relocated to Canada if that happens and the resulting world is something like in Code Geass? What if it had arisen during the Napoleonic Wars?
Or, what if it arises now? We know that there's a micronation calling itself Sealand in the area. Do you think they have a claim to the land? Or would the neighbouring powers fight over the landmass and ultimately dissolves the EU? Or maybe a new nation is declared by them so that they wouldn't fight over it? What about the Norwegian fishing treaties?
Well, there are so many possibilities in how our world would've turned out if the land hadn't sunk. But in a world where we are afraid of icebergs melting and flooding coastal cities due to global warming, one must remember that in the past, humans have experienced a disappearance of a hugely populated landmass the size of California in the middle of Europe. So I guess the moral of the story is, fuck coastal people! :p
Lastly, have a picture of a helmet from Star Carr from around the time when Doggerland existed. Because at the time, Star Carr was connected to Doggerland, so it's possible that Doggerlanders might've worn it too

Also, a short introductory video about Doggerland