We say the USA, the UK, the Czech Republic, the West Indies, the Philippines, the Netherlands but we don’t use the India, the Pakistan, the China, the South Korea, the Japan, the Taiwan, the Indonesia etc. Do you people wanna know why some countries use ‘the’ ? Here is the explanation briefed in points:-
1) Many English scholars say that the countries which consist the words ‘states’, ‘republic’, ‘kingdom’, ‘federation’ with their names, article ‘the’ is used. For example:- The United States, The United Kingdom, The Czech Republic, The Russian Federation etc.
2) ‘The’ is also used with the countries consisting many Islands. For example:- The Bahamas, The Philippines, The Maldives, The West Indies etc.
3) Some explain that countries like the United States of America and the United Kingdom also carry the definite article because they are compound nouns with adjectives.
4) One of the answers on Yahoo website gives this explanation; Now, America is the name of the large landmass which was found in the 16th century. “North America” and “South America” are the proper nouns, names for two continents. So we won’t use “the” before them.
In North America, 13 colonies united to form a nation. So they called themselves “the United States of America”. The was used as a large no. of states were NOT a part of it. So it was used to distinguish.
Similarly “United Kingdom” could be any kingdom which was formed by uniting two or more kingdoms. So “the United Kingdom” would specifically refer to the United Kingdom of Great Britain and Northern Ireland.
But India is a proper name. 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.