Geneticists tell us the entire human race originated from a single tribal group of around 200 people who migrated from Africa into Arabia about 80,000 years ago. About 10,000 years ago, their descendants, by then numbering around 5 million, began to form agricultural settlements, leading to the first kingdoms. In more recent centuries, the earliest nation-state emerged. By 1920, around 1.7 billion of their descendants lived in fewer than 80 countries.
That consolidation has now ended. In the last century, dozens of new nations have been created, mostly formed along religious or ethnic lines. That's why nearly 200 countries exist today.
There's a reason for this growing number of sovereignties. When they can, humans often choose to live independently in small and internally cohesive groups.
The UK could be the next example of the end of consolidation. The UK consists of a handful of Caribbean territories, along with four countries: England, Scotland, and Wales, which comprise the island of Great Britain, and Northern Ireland.
In June, UK voters chose to exit the EU. That vote could set off a chain of events that will tear apart the UK. Separatists in Northern Ireland now are speaking of a divorce from Great Britain, and the majority of Scottish voters currently favor separating from the UK. While Scotland's pro-independence side lost in a 2014 referendum, polls indicate that if another vote were held today, voters would approve secession. That would leave England and Wales as the last remnants of the UK.
Separatist parties in Belgium, Croatia, the Czech Republic, Italy, and Spain likewise want to create their own independent states, to name just a few movements across Europe.