behandeln
to treat
To deal with a person or thing in a particular way.
Man sollte alle Menschen mit Respekt behandeln.
One should treat all people with respect.

to treat / to deal with
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to treat
To deal with a person or thing in a particular way.
Man sollte alle Menschen mit Respekt behandeln.
One should treat all people with respect.

'Behandeln' (to treat / to deal with) is an inseparable verb because it begins with the prefix 'be-'. The prefix makes the verb 'handeln' (to act / to trade) transitive, which means that 'behandeln' always requires an accusative object.
Ich behandle dieses Thema in meinem nächsten Vortrag.
I deal with this topic in my next lecture.
The exact meaning of 'behandeln' (to treat / to deal with) depends strongly on the object. You treat people, illnesses, topics, or materials. The context makes clear which meaning is intended.
Der Chef behandelt seine Mitarbeiter fair.
The boss treats his employees fairly.
When the object is a person, 'behandeln' (to treat) describes the way they are dealt with. Often an adverb or a 'wie' (like/as) clause is added to describe the manner.
Er behandelt seinen Hund wie ein Familienmitglied.
He treats his dog like a family member.
In a medical context, 'behandeln' (to treat) is often used with the preposition 'mit' (with) to name the medication or method. The object is the illness or the patient.
Die Ärztin behandelt die Grippe mit Ruhe und viel Tee.
The doctor treats the flu with rest and lots of tea.
When topics are involved, the subject is often a book, a film, or a lecture. The verb then describes which topic is dealt with in it.
Dieses Buch behandelt die Geschichte des 20. Jahrhunderts.
This book deals with the history of the 20th century.
to act / trade
'handeln' and 'behandeln' can both have to do with a topic or with dealing with something. The most important difference lies in how they are used. 'handeln' often means that someone actively does something. With 'von', it also describes what a book, film, or conversation is about. 'behandeln' means that you deal with a person, thing, or topic in a particular way. With topics, it is often used for classes, texts, or discussions. Learners easily confuse the words because both can fit with topics: a film 'handelt von' a problem, but in a course you 'behandelt' a problem.

Im Deutschkurs behandeln wir heute das Thema Wohnen.
In German class, we are covering the topic of housing today.
Der Film handelt von einer Familie, die in eine neue Stadt zieht.
The film is about a family that moves to a new city.