Learn Hardcore Japanese: nakama to ryokou wo simasita.

Breakdown of nakama to ryokou o shimashita.

Why is と used after 仲間?

Here, と means with.

So:

In this sentence, と marks the person or people you did the action together with.

Compare:

So と is not the topic marker here; it shows accompaniment.

What does を do in this sentence?

を marks the direct object of the verb.

Here, the object is 旅行:

This works because 旅行 is a noun that can combine with する to make a verb-like expression:

So を shows that 旅行 is the thing being done.

Why does the sentence use 旅行をしました instead of just a verb meaning traveled?