Why the is not used before country?
We say the United States, the United Kingdom, the Czech Republic, the West Indies, the Philippines, and the Netherlands because they are compound nouns with adjectives but not India, France, China, South Korea, Japan, Germany, or Indonesia.
The is also used with countries whose names include the words states, kingdom, or republic: My sister lives in United States . My sister lives in the United States .
Countries like the United States of America and the United Kingdom also carry the definite article because they are compound nouns with adjectives. Professor Liberman says the habit of putting "the" in front of place names is heard throughout the English-speaking world and is common to Germanic and Romance languages.
We do not use 'the' with the names of countries. So, 'the' will not be used before India, Pakistan, China, Sri Lanka, Indonesia. Exception: if the countries have the words 'states, kingdom, republic' we use 'the' before their name. For example: The United States of America, The United Kingdom, etc.
India only refers to the country India. You don't need to specify “which India?”. In the case of USA and UK, now, they are proper names but as the names also form a description rather than just the names, “the” is used.
America is named after Amerigo Vespucci, the Italian explorer who set forth the then revolutionary concept that the lands that Christopher Columbus sailed to in 1492 were part of a separate continent.
With the names of countries and continents
In these instances we do not use the articles at all, BUT if the country is made up of different parts or if the name is taken from common nouns, for example USA, UK, UAE, then we use the article the and say the USA, the UK, the UAE, the Czech Republic, The Netherlands.
'An' is used before words which begin with a vowel sound. Note that we are talking about sounds and not spelling. For example the word "European" begins with the vowel letter 'e' but it is pronounced with the consonant sound / j /. Therefore we say and write, "He's British but he thinks of himself as a European."
Rule 1 is that we use 'The' if the county's name includes a common noun. Rule 2 is 'The' is used before any country name if the name contains 'of'. Rule 3 says we use 'The' if the country is an island country.
The preposition en always comes before the name of a country if it is feminine and before masculine countries if they start with a vowel.
Why do Brits not use the?
It is not necessary to say "go to the hospital" or "go on the holiday", when talking in a general sense. Use of the word 'the', means that the sentence is in a particular sense. A reference to one, particular example. "go to the hospital" will mean going to one, particular hospital.
Drum roll, please: Turns out, no countries in the world start with the letters W or X.