zusammenhängen mit
to be related to
To have a connection or a causal, logical, or thematic relationship to something.
Die hohe Arbeitslosigkeit hängt mit der schwachen Konjunktur zusammen.
The high unemployment is related to the weak economy.

to be connected / to be related
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to be related to
To have a connection or a causal, logical, or thematic relationship to something.
Die hohe Arbeitslosigkeit hängt mit der schwachen Konjunktur zusammen.
The high unemployment is related to the weak economy.

'Zusammenhängen' (to be connected/related) is a separable verb. In a main clause, the prefix 'zusammen' stands at the end, while in a subordinate clause it remains attached to the verb.
Diese beiden Probleme hängen eng zusammen.
These two problems are closely connected.
The verb consists of 'zusammen' (together) and 'hängen' (to hang). Literally, it means 'to hang together', which describes both the physical and the logical connection well.
Die Puzzleteile hängen fest zusammen.
The puzzle pieces are firmly connected.
When referring to a logical or causal connection, the preposition 'mit' + dative is almost always used.
Sein Verhalten hängt mit seiner Kindheit zusammen.
His behavior is related to his childhood.
To ask about a connection, the questions 'Wie hängt das zusammen?' (How is that connected?) or 'Womit hängt das zusammen?' (What is that connected to?) are often used.
Womit hängt der plötzliche Erfolg der Firma zusammen?
What is the company's sudden success related to?
to have
'mit etwas zu tun haben' (to have to do with something) and 'zusammenhängen mit' (to be related to) both describe a connection between things, topics, or events. 'Mit etwas zu tun haben' is more general and often more colloquial. It can mean that something concerns a topic or is connected with it. 'zusammenhängen mit' puts more emphasis on a factual, logical, or causal connection. When you want to explain why something happens or what something is influenced by, 'zusammenhängen' is often more precise. In conversation, 'hat mit ... zu tun' sounds very natural; in explanations, 'hängt mit ... zusammen' sounds more precise.

Am Abend erklärt mein Kollege, dass die Verspätung mit dem Streik zusammenhängt.
In the evening, my colleague explains that the delay is related to the strike.
Der Arzt sagt, die Schmerzen haben mit dem alten Unfall zu tun.
The doctor says the pain has to do with the old accident.