The US requires an article in German because it is a plural (United States). Switzerland and Turkey require it because they are female. Ukraine is female too a

The US requires an article in German because it is a plural (United States). Switzerland and Turkey require it because they are female. Ukraine is female too and therefore "die Ukraine" is correct. Most state names in German are neuter and go without article. Some state names can be used as male with article (der Kongo) or neuter without (Kongo). Iran is the most common example of this category, in the news "in Iran" and "im Iran" are both used frequently