Only in this very specific case (saying “from one country to another“) should you only use the “à/au/à l’” preposition.

For masculine country names beginning with a consonant, you will say “au“

ex: “du Japon au Brésil”, “du Japon au Pérou”

For feminine country names beginning with a consonant, you will say “à la“

ex: “du Japon à la Belgique”, “du Japon à la Colombie”

For all country names beginning with a vowel, you should use “à l’“

ex: “du Japon à l’ Angleterre”, “du Japon à l’ Espagne”

There is no easy way to remember whether a country is masculine or feminine.
Native speakers just learn it by heart…

And as if it was not complicated enough, there are exceptions to this rule.
Some country names, mostly islands but also plural countries like the U.S., act like city names.
Then you just use “à“, or “aux” if it is an archipelago or plural.

ex: “du Japon à Cuba”, “du Japon à Madagascar”, “du Japon
aux Philippines”, “du Japon aux États-Unis”

And again, not all island countries act this way. Ireland, Australia, and Sri Lanka for instance behave like normal country names. You just have to learn the exceptions.

If you want to say you are in a country, then it is another rule: the “en/au/à” rule.

Country names beginning with a consonant take “au“, feminine country names or country names beginning with a vowel take “en“, and islands and plural countries exceptions take “à” or “aux“.

ex: Je suis en Belgique (feminine), en Argentine, au
Congo (masculine with a consonant), à Cuba, aux États-Unis.

You need to learn the article (or the absence of it) in order to guess how to say from… to. Beware: I’m only talking about that specific context. I’m not talking about position (I live in France), destination (I go to France), or origin/source (I’m from France). It would be a different translation to say I travel from Japan to France or I have moved house from Japan to France. Here is only about the distance.

• La (feminine) = de la… à la…

La France, la Birmanie

De la Birmanie à la France

• Le (masculine) = du… au…

Le Japon, le Congo

Du Japon au Congo

• L’ = de l’… à l’… (masculine or feminine with an apostrophe, starts with a vowel so le and la become l’, the only exception is le Yémen which is used as masculine above)

L’Allemagne (f.), l’Iran (m.)

De l’Allemagne à l’Iran

• Les = des… aux… (plural)

Les États-Unis, les Pays-Bas

Des États-Unis aux Pays-Bas

• No article = de… à…

Cuba, Israël

De Cuba à Israël, d’Israël à Cuba (note the d’ because of the vowel)

As you can see, there is no use of en. Haïti is in the last group, so it’s D’Haïti au Japon (the h is silent in Haïti, so it’s like it is starting with the vowel a) and Du Japon à Haïti.

Bonus: is there a way to know if a country is feminine, masculine or else? It seems that yes:

• Feminine countries end by a e (la France, la Colombie, l’Argentine…), except: le Mexique, le Zimbabwe, le Cambodge and le Mozambique.
• Masculine countries end by a consonant or another vowel (le Canada, l’Uruguay, le Maroc…).
• Few countries are plural (les États-Unis, les Pays-Bas).
• Some islands (Cuba, Madagascar) and Israël have no article (hard to guess).