UK, Ireland /
What's the rule on 'the UK' but just 'GB'? [60]
I'm surprised there's confusion over this. If we look at the list presented:
The Soviet Union, The United States, The Czech Republic, The United Kingdom, Great Britain
can you spot the odd one out? One of these is not a country.
If the name you are using contains a political state word (Union, State, Republic, Kingdom) then we need the definite article. Attaching "The" really doesn't have anything to do with the country being some sort of plural as a political entity. If it's a group of islands then sure (The Bahamas, the Maldives, The Canaries) but we're referring to the geographical idea of a group, not the political one; the same way we talk about groups of mountains (The Alps, The Tatry) but not individual ones (Mont Blanc, Kasprowy Wierch.)
And Great Britain is NOT a country. It is a geographic land mass, not a political one, which contains three countries that make up a substantial portion of the political entity, The United Kingdom. The confusion comes from the car sticker 'GB', which makes people think that Britain is a country, like PL and DE do, but Northern Ireland have their own symbol, 'NI', so that the Irish know which particular car to attach their bombs to*.
The use of "-lands" in the name of the country (as opposed to just -land) is the background behind this idea of "plural countries", and that's why we have The Netherlands. And there are other countries that still defy sound explanation (The Gambia and The Congo are just two), but The Ukraine, once it gained its independence, cleaned up its ungrammatical international reputation, and politely asked to be called Ukraine. The End.
*this is a joke. A tasteless one, but a joke nonetheless.