Until a few decades ago, Ukraine was almost always referred to as the Ukraine. Then people started dropping the definite article, and now you almost never see it. What gives?
The the has stirred up a lot of strong resentment in Ukraine. The feeling is that the definite article’s heavy use during the era of the Soviet Union by Russians and Westerners alike belittled, intentionally or not, Ukrainians, and demoted Ukraine from a country unto itself to a mere Soviet holding, a border region of the U.S.S.R.
Most historians and linguists agree that the name Ukraine comes from the Slavic ukraina, meaning “borderlands.” Since many countries whose names derive from a geographical feature or factor have a definite article—“the Philippines” referring to the Philippine islands, “the Netherlands” meaning “the lowlands”—the Ukraine makes sense in terms of “the borderlands.”
There’s a little bit of uncertainty about the etymology of Ukraine, though. A few modern Ukrainian historians trace it to the same root word, but with a different meaning, variously “homeland,” “country,” “land,” “separated piece of land” or “separated part of the tribe,” depending on which historian you’re asking and which sources they’re looking at. The “borderlands” etymology appears to have the most historical support, but if that meaning doesn’t hold up, then the logic for the definite article likewise falls apart.
Since Ukraine gained independence from the Soviet Union, use of the article has declined steadily, in part because of the Ukrainian government expressing their preference for dropping it. In the Google ngram searches below, you can see the Ukraine fall and Ukrainerise (sharply) right around the country’s declaration of independence in 1991, both in reference to the country, and (more so) to things in it.