fordern
to demand
To demand or claim something emphatically, often because one believes one has a right to it.
Die Mitarbeiter fordern eine Gehaltserhöhung von fünf Prozent.
The employees are demanding a five percent pay raise.

to demand / challenge
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to demand
To demand or claim something emphatically, often because one believes one has a right to it.
Die Mitarbeiter fordern eine Gehaltserhöhung von fünf Prozent.
The employees are demanding a five percent pay raise.

The verb 'fordern' (to demand/challenge) belongs to the word family of the noun 'die Forderung' (demand). A 'Forderung' is what one demands emphatically.
Die Forderung nach besseren Arbeitsbedingungen wurde von allen unterstützt.
The demand for better working conditions was supported by everyone.
When demanding something from someone, the structure is often: 'etwas (Akkusativ) von jemandem (Dativ) fordern' (to demand something from someone). Alternatively, a subordinate clause with 'dass' (that) can follow.
Die Kunden fordern vom Unternehmen eine Entschuldigung.
The customers are demanding an apology from the company.
In the meaning 'herausfordern' (to challenge), the subject is often a task, job, or problem. Typical objects are then abstract things like 'Konzentration' (concentration), 'Kraft' (strength), 'Kreativität' (creativity), or 'Geduld' (patience).
Ein Marathonlauf fordert Ausdauer und mentale Stärke.
Running a marathon demands endurance and mental strength.
This meaning is used almost only in connection with negative events such as accidents, wars, or natural disasters. The subject is the event, and the object is usually 'Opfer' (victims), 'Todesopfer' (fatalities), or 'Leben' (lives).
Der schwere Verkehrsunfall forderte drei Verletzte.
The serious traffic accident left three people injured.
to pass / consist / exist
'bestehen auf' and 'fordern' can both mean that someone demands something very clearly. 'fordern' mainly names the demand itself: someone demands money, rights, help, or a decision. 'auf etwas bestehen' (to insist on something) emphasizes more strongly that the person is not giving in and wants exactly that thing. The words can be confused because both sound emphatic. 'fordern' works well for public or clear demands. 'bestehen auf' fits when someone sticks to a condition or rule.

Die Mitarbeiter fordern mehr Zeit für die Vorbereitung.
The employees are demanding more time for preparation.
Der Kunde bestand auf einer schriftlichen Bestätigung.
The customer insisted on written confirmation.