There are only two groups of countries which require the article in English: Those with plural names such as the United States or the Netherlands. The others have names with adjectival or compound forms which require the article, such as the United Kingdom, the Dominion of Canada, or the Ukrainian SSR.
English grammar does not require a definite article before the names of singular countries such as England, Canada or Ukraine.
Source: "Ukraine" or "the Ukraine"?
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