Wir prüfen alles, denn der Anschlussverlust veränderte den Reiseverlauf.

In German, a comma is normally used before denn when it connects two full main clauses.

Here, both parts could stand on their own:

• Wir prüfen alles.
• Der Anschlussverlust veränderte den Reiseverlauf.

Because denn links these two complete clauses, the comma is required.

Denn means because here, but it works differently from weil.

• denn is a coordinating conjunction
• weil is a subordinating conjunction

That means word order changes:

• Wir prüfen alles, denn der Anschlussverlust veränderte den Reiseverlauf.
• Wir prüfen alles, weil der Anschlussverlust den Reiseverlauf veränderte.

After denn, the clause keeps normal main-clause word order. After weil, the verb usually goes to the end.

So denn and weil can both mean because, but they do not behave the same grammatically.

Because denn does not create a subordinate clause.

In the second clause:

• der Anschlussverlust = subject
• veränderte = verb
• den Reiseverlauf = object

So the order stays like a normal main clause: subject + verb + object.

This is one of the most important things to remember about denn: it means because, but it does not trigger subordinate-clause word order.

This is about case.

• der Anschlussverlust is the subject of veränderte, so it is in the nominative case.
• den Reiseverlauf is the direct object, so it is in the accusative case.

Both nouns are masculine singular, so the article changes like this:

• nominative masculine: der
• accusative masculine: den

So:

• der Anschlussverlust = the missed/lost connection as the doer of the action
• den Reiseverlauf = the travel itinerary as the thing affected

In German compound nouns, the last part usually determines the gender.

Anschlussverlust is made up of:

• Anschluss = connection
• Verlust = loss

The final element is Verlust, and der Verlust is masculine.
So the whole compound is also masculine:

• der Anschlussverlust

This same rule works with many German compounds.

It is a compound noun:

• Anschluss = connection, often a travel connection such as a train, bus, or flight connection
• Verlust = loss

So Anschlussverlust literally means loss of a connection.
In travel context, it often refers to a missed connection or the fact that a planned onward connection was lost.

A learner should also know that German often uses compact compound nouns where English may prefer a phrase.

The sentence mixes time frames:

• Wir prüfen alles = we are checking everything now / in the present situation
• der Anschlussverlust veränderte den Reiseverlauf = the missed connection changed the itinerary earlier

This is completely natural. A past event explains a present action.

So the idea is: We are checking everything now because something happened earlier.

Veränderte is the simple past (also called the preterite) of verändern.

German often uses the preterite more in writing, formal narration, reports, and similar contexts.
So:

• veränderte = simple past
• hat verändert = present perfect

Both can often be translated the same way in English:

• der Anschlussverlust veränderte den Reiseverlauf
• der Anschlussverlust hat den Reiseverlauf verändert

The first one sounds a bit more written or report-like.

The infinitive is verändern, meaning to change or to alter.

Veränderte is:

• 3rd person singular
• simple past / preterite

So it matches der Anschlussverlust:

• der Anschlussverlust veränderte

That means: the missed connection changed ...

Because alles already functions as a pronoun meaning everything.

So:

• Wir prüfen alles = We check everything / We are checking everything

You do not normally say das alles in this basic structure unless you are emphasizing something in a different way.

In German, all nouns are capitalized.

So in this sentence:

• Anschlussverlust
• Reiseverlauf

are capitalized because they are nouns.

This is a standard rule of German spelling and is very different from English.

Often yes, but it depends on context.

Prüfen usually means:

• to check
• to examine
• to inspect
• to verify

In this sentence, Wir prüfen alles suggests something like:

• we are checking everything carefully
• we are reviewing everything
• we are verifying all details

So check is a good translation, but prüfen can sound a bit more thorough than casual English check in some contexts.

Yes, but the word order would change.

With denn:

• Wir prüfen alles, denn der Anschlussverlust veränderte den Reiseverlauf.

With weil:

• Wir prüfen alles, weil der Anschlussverlust den Reiseverlauf veränderte.

The meaning is very similar, but:

• denn sounds a bit more formal or written in some contexts
• weil is very common in everyday speech

The key grammar point is: weil sends the verb to the end of its clause, while denn does not.