Na de discussie kwamen we erachter dat we eigenlijk minder oneens waren dan we dachten.

Here, erachter komen means to find out, to discover, or to realize.

So:

Na de discussie kwamen we erachter dat...
= After the discussion, we found out that...

You should not translate it word for word. Literally, erachter looks like behind it, but as an expression, erachter komen is idiomatic.

Because Dutch main clauses usually follow the verb-second rule.

The sentence starts with Na de discussie, which takes the first position. That means the finite verb must come next:

• Na de discussie kwamen we erachter...

If there were no opening phrase, you would get:

• We kwamen erachter...

So the word order changes because Na de discussie is placed first.

In this sentence, er is part of the fixed expression erachter komen.

It points forward to the content that is introduced by dat:

• We kwamen erachter dat...

A natural English equivalent is just we found out that...
English does not need a separate word for this er.

This kind of forward reference is very common in Dutch.

Dat introduces the clause containing what was found out.

So:

• we kwamen erachter = we found out
• dat we eigenlijk minder oneens waren dan we dachten = that we were actually less in disagreement than we thought

In English, that can often be left out:

• We found out (that) we...

In Dutch, dat is much more commonly kept.

Because Dutch subordinate clauses often put the verb near or at the end.

After dat, you get subordinate word order:

• dat we eigenlijk minder oneens waren

And after dan plus a clause, Dutch also commonly puts the verb at the end:

• dan we dachten

So this is normal Dutch syntax, even though it may feel unusual if you are used to English word order.

Oneens means in disagreement or not agreeing.

Dutch often uses an adjective with zijn where English uses a verb:

• We are in disagreement → Dutch: We zijn oneens
• Natural English: We disagree

A very common pattern is:

• het eens zijn = to agree
• het oneens zijn = to disagree

In this sentence, oneens is being used as an adjective after waren.

Minder oneens literally means less in disagreement.

It does not necessarily mean full agreement. It suggests that the difference between the two sides was smaller than expected.

So the idea is:

• We thought we disagreed a lot.
• After discussing it, we realized the disagreement was not as big as we had thought.

A good natural English rendering is:

• we actually disagreed less than we thought
• or we were actually less far apart than we thought

Eigenlijk often means actually, really, or in fact.

Here it signals a correction of an earlier impression:

• we thought X
• but actually, the truth was a bit different

So eigenlijk adds the sense of it turned out, in reality...

Because Dutch uses dan after a comparative such as:

• meer = more
• minder = less
• groter = bigger
• kleiner = smaller

So:

• minder oneens dan we dachten = less in disagreement than we thought

By contrast, als is used in comparisons of equality:

• even groot als = as big as

So:

• groter dan = bigger than
• even groot als = as big as

The simple past is very normal in Dutch when telling what happened or describing a past situation.

So this sentence has a natural narrative feel:

• Na de discussie kwamen we erachter...

You could also say:

• Na de discussie zijn we erachter gekomen dat...

That perfect-tense version is also correct, but it sounds a bit more result-focused or conversational in some contexts.

The version with kwamen is completely natural and often feels slightly smoother in storytelling or written narration.