Tri landoj aliĝis al la unio.

In Esperanto, nouns normally still take the plural ending -j even when a number is present.

So:

• tri landoj = three countries
• du urboj = two cities
• kvin libroj = five books

This is different from English, where the number alone often makes the plural obvious. In Esperanto, the plural marking is still required.

If there were an adjective, it would also become plural:

• tri grandaj landoj = three big countries

The ending -is marks the past tense in Esperanto.

So:

• aliĝi = to join
• aliĝas = joins / is joining
• aliĝis = joined
• aliĝos = will join

This is one of Esperanto’s regular verb endings:

• -as = present
• -is = past
• -os = future
• -us = conditional
• -u = command / wish
• -i = infinitive

Because aliĝi is a single verb in Esperanto, meaning to join or to become affiliated.

It is not understood as the preposition al plus a separate verb in the sentence. You should learn aliĝi as a vocabulary item.

In this sentence:

• aliĝis = joined
• al la unio = to the union

So the verb is aliĝi, and it happens to be followed by the preposition al.

Because aliĝi is commonly used with al to show what someone or something joins.

So:

• aliĝi al organizo = join an organization
• aliĝi al grupo = join a group
• aliĝi al la unio = join the union

This is similar to how English verbs often go with particular prepositions. A learner usually just has to remember that aliĝi is used with al.

La is the definite article, meaning the.

So la unio means the union, not just a union or union in a general sense.

Esperanto uses la when the noun is definite, specific, or already known from context. If the sentence is talking about a particular union, la is natural.

Also notice that Esperanto has only one article: la. There is no separate word for English a/an.

Because there is no direct object here.

• Tri landoj is the subject, so it does not take -n.
• la unio comes after the preposition al, and nouns after prepositions normally do not take -n.

So the structure is:

• Tri landoj = subject
• aliĝis = verb
• al la unio = prepositional phrase

In Esperanto, the accusative -n is mainly used for direct objects and for some other special uses, but not normally after a preposition like al.

Yes. Esperanto word order is more flexible than English, because endings make the grammar clearer.

The neutral order here is:

• Tri landoj aliĝis al la unio.

But you could also say:

• Al la unio aliĝis tri landoj.

That version might put more focus on al la unio or sound a bit more stylistic.

Even so, the basic subject + verb + complement order is very common and usually best for learners.

Because tri landoj simply means three countries in a general counting sense.

If you say:

• tri landoj = three countries
• la tri landoj = the three countries

then la makes them definite and specific.

So the sentence without la suggests three countries, but not necessarily a previously identified set of exactly those three.

A simple learner-friendly pronunciation is roughly:

ah-LEE-jees

More exactly:

• a as in father
• li with stress here: a-LI-ĝis
• ĝ sounds like j in judge
• s is always a plain s, never z

The stress in Esperanto normally falls on the second-to-last syllable, so in a-li-ĝis, the stress is on li.

Yes. Esperanto does not require a subject pronoun if the subject is already a noun phrase.

Here, Tri landoj is the subject, so nothing else is needed.

Compare:

• Ili aliĝis al la unio. = They joined the union.
• Tri landoj aliĝis al la unio. = Three countries joined the union.

Both are complete sentences.