En slump is 'a chance', 'a coincidence', or 'an accident'. Hear how it sounds below:

There are several ways to say “it happened by chance” or “it happened by accident” using slump. The two most common are to say: det var en slump (att) or to say something happened av en slump. 

Don't forget the article (en), which is easily done if you're used to the English phrases 'by chance', 'by accident' or 'at random'. Let's take a look.

Det var en slump – It was an accident/it happened by chance

Det är en slump att (det här händer nu) – It is by chance that (this is happening now)

Ön upptäcktes av en slump – The island was discovered by chance

Jag blev rik nästan av en slump – I got rich almost by accident

You can reinforce it by using words like ren (pure): det var en ren slump! or show how you feel about it by adding an adjective like lycklig (happy) or olycklig (unhappy): Jag träffade henne av en lycklig slump (I met her by happy coincidence). 

And as a one-word alternative, you can use the adjective slumpmässig or the adverb slumpmässigt.

For example:

Denna utveckling är inte slumpmässig – This development is not random

Personerna har valts slumpmässigt – The people were chosen randomly

If you want to stress that something was intentional, there are two ways to use slump:

Det är ingen slump att (alla har sagt samma sak) – It's no coincidence that (everyone said the same thing)

Det är inte en slump att (du föddes) – It's not by chance that (you were born)

The second example using inte places a strong emphasis on the negation, perhaps if you're challenging a widely held view. 

We're looking at this word today after the director of Sweden's Public Health Agency said that Sweden was worse hit by the coronavirus outbreak than its Nordic neighbours av en slump (at random).

The assertion in an interview with Svenska Dagbladet has ignited debate over Sweden's strategy focused on voluntary measures compared to the stricter lockdowns in Denmark and Norway, and the perceived lack of accountability at the agency that has led the national coronavirus response.