When to use definite article with country/region and au préalable

Question

When do you use the definite article with countries and regions?There's a kwiziq lesson about this: Using le, la, l', les with continents, countries & regions names (definite articles)

But in the text, country and region names are never accompanied by the definite article. E.g., "Duché de Bretagne," "royaume de France," "couronne de France," etc.

Also, I translated "beforehand" as "à l'avance" instead of "au préalable," which I thought were the same thing, but it wasn't one of the accepted answers.

Accepted Answer

It is only with feminine countries/regions that the article (la or l’) is dropped with the preposition ‘de’ (from/of) and even then it is not dropped in all cases. 
This question was asked recently in regard to La Guadeloupe and the first link below was posted in response as well.
Je viens du Canada; produit des États-Unis. 
https://www.intermarkls.com/single-post/2015/07/11/the-french-they-never-taught-you-22-de-france-or-de-la-france
 
https://progress.lawlessfrench.com/revision/grammar/say-where-you-come-from-with-venir-de-d-du-des-country-state-region

Answer

Bonjour Gee,
Further to Maarten's reply, with expressions such as "duché de Bretagne / royaume de France / couronne de France", you do not use "de la" as they consider the geographical location, aka “from”.

Les vins d'Espagne = The Spanish wines
Les rois de France = The French kings

Attention: masculine or plural countries - use "du / des"

Les villes du Portugal = The cities from Portugal
Les vins des États-Unis = The wines from the USA

If you talk about where it "belongs to", then you will use "de + [article défini]":

La capitale de la Russie = Russia's capital city
Les problèmes économiques de l'Espagne = Spain's economic problems

I hope this is helpful.
Bonne journée !

Answer

If you are talking about the country per se -- in particular if the country is the subject of the sentence or the COD -- then the article is needed.

When saying which country you're coming from, whether you use the article depends on the country: no article with feminine countries, all other countries (masculine and plural) use the article.

La France est membre de l'Union européenne.

J'aime les Etats Unis.

J'ai vécu en France pendant 5 ans.

Mon ami vient de France.
Mon ami vient du Monaco.
Mon ami vient des Etats Unis.