1765: Articles in Countries' Names
There are three main reasons why a country would have an article in the name. For many, it is a translation, like 'the Netherlands' (the lowlands), 'the Ukraine' (the borderlands), and in the case of other countries it refers to an island chain, like 'the Maldives' or 'the Philippines', or if the country was named after something else, e.g. 'the Lebanon mountains', 'the Sudan desert'. There are some exceptions, like 'the Gambia', which changed its disambiguate from 'Zambia', or 'the UK' which is part of a phrase. Many of these uses are unofficial, but it should be noted that there isn't a reason that some other countries don't have an article, or why English speakers have mostly abandoned them.