The 1990s reshaped a huge chunk of it

The Soviet Union's collapse in December 1991 alone created 15 new countries, from the Baltic states (Estonia, Latvia, Lithuania) to the five Central Asian "-stans" that most people would struggle to order correctly on a map even now.

Yugoslavia's breakup created seven more (Slovenia, Croatia, Bosnia and Herzegovina, Serbia, Montenegro, North Macedonia, Kosovo) over roughly a decade of conflict that ran from 1991 through the Kosovo War ending in 1999.

If a country in Eastern Europe feels unfamiliar, there's a real chance it simply didn't exist in its current form 35 years ago.

Czechoslovakia split peacefully into the Czech Republic and Slovakia on 1 January 1993, in what became known as the "Velvet Divorce," negotiated by politicians rather than fought over, and one of the few modern separations achieved without violence.

Montenegro left the state union with Serbia by referendum in May 2006, with just over 55% voting for independence, a wafer-thin margin against the 55% threshold the EU had insisted on beforehand.

If your mental map was formed from an older atlas, this region is where it's most out of date.

German reunification in 1990 ran the process in reverse: two countries became one, with East Germany's five states absorbed into the Federal Republic rather than a new state being founded.

Yemen did the same the same year, uniting North and South Yemen after decades apart, a rare instance of unification succeeding where so many separatist movements have failed.

Colonial-era borders still explain a lot of Africa's map

Many African borders were drawn in European negotiations in the late 1800s. The 1884-85 Berlin Conference was the most notorious of them, with fourteen European powers carving up the continent without a single African representative in the room, and with little regard for existing ethnic or linguistic territories.

That's part of why some borders look like ruler-straight lines rather than following rivers or mountain ranges the way older borders elsewhere tend to.

The straight lines are a genuine navigational aid when learning the map, but they're also the reason several African countries are hard to distinguish by shape: a rectangle drawn at a conference table looks much like the next rectangle drawn at the same table.

Egypt's southern border with Sudan, Namibia's Caprivi Strip, and the near-identical northern edges of Chad, Niger and Mali are all straight-ruled legacies of that era.

Decolonisation in the mid-20th century mostly kept those lines rather than redrawing them. The Organisation of African Unity formally endorsed keeping colonial-era borders in 1964, on the reasoning that reopening them would cause more conflict than it solved.

It's a decision historians still argue about, since it locked in borders that had split some ethnic groups across two or three countries and combined others that had little in common beyond a shared coloniser.

Some splits are recent enough to matter for the app specifically

South Sudan became the world's newest widely-recognised country on 9 July 2011, splitting from Sudan after a referendum in which more than 98% of voters chose independence, following decades of civil war.

East Timor (Timor-Leste) became independent in May 2002, after a UN-administered transition that followed Indonesia's withdrawal in 1999. If you're using an older mental map, these are the gaps most likely to trip you up in Map the Planet.

Kosovo declared independence from Serbia in February 2008 and is recognised by roughly half of UN members, which is why it appears on some maps and not others. Serbia, Russia, China and Spain are among the notable non-recognisers, each for different reasons.

Eswatini renamed itself from Swaziland in 2018, on the 50th anniversary of its independence from Britain, and North Macedonia settled a decades-long naming dispute with Greece in 2019 under the Prespa Agreement, where no borders moved but the label changed from "Macedonia" to "North Macedonia" to satisfy Greek objections tied to its own northern region of the same name.

Sudan itself had already been Africa's largest country by area before the 2011 split; Algeria took over that title afterwards, a fact that trips up plenty of otherwise strong players.

Borders that follow rivers and mountains tend to be older

Where a border follows a coastline, watershed or mountain range, it usually predates modern surveying and reflects how people actually moved and settled. Consider the Pyrenees between France and Spain (formalised by the Treaty of the Pyrenees in 1659), the Andes between Chile and Argentina, the Rio Grande between the US and Mexico following the 1848 Treaty of Guadalupe Hidalgo.

Where it's straight, it was almost certainly drawn on paper, often far from the territory in question. That single distinction lets you read a lot of history straight off a map without opening a book.

The US-Canada border is the most famous example of a mostly-straight, mostly-negotiated line: the 49th parallel was set by an 1818 treaty and extended westward over subsequent decades, making it one of the longest deliberately straight borders on Earth, broken only where the Great Lakes and a handful of surveying quirks get in the way.

Border disputes that are still technically unresolved

Not every line on the map is settled, even if games and atlases have to pick one version to display. India and Pakistan both claim the whole of Kashmir while administering different parts of it. China and India dispute stretches of their Himalayan border, notably Arunachal Pradesh.

South Sudan and Sudan still argue over the oil-rich Abyei region. Western Sahara remains partly administered by Morocco and partly claimed by the Sahrawi Arab Democratic Republic, and its status is one of the longest-running unresolved decolonisation cases at the UN.

None of this is likely to come up in a casual quiz, but it's worth knowing that "the map" is really a snapshot of the most widely accepted version of an ongoing negotiation, not a finished document.