Others have made some valid points here. I'm sure there are many reasons, some unique to circumstances, but here is something I've noticed, that doesn't make sense, but it seems to be true in some instances. - Jealousy - For example, if a woman stands up to a man for making sexually inappropriate remarks or actions, sometimes other women will be jealous that those remarks or actions weren't aimed at them, so they minimize the woman who was the target (victim) of those remarks or actions, instead of standing with her, they stand against her. I have seen this happen in my own life.

There may be cases where this happens, but each one must be looked at on its own and the various circumstances in which it happens. I can’t say that I see a whole trend here....do you think as a rule women take the part of men against other women? If you do it is not something I have noticed as a generality. I think your whole premise is rather sweeping when you ask “why are women so quick to minimise other women in instances of conflict”? I was not aware that this is usually the case., although I accept that in some cases it may be true. Without knowing details of individual instances there is no definitive answer to your question, as the reasons will prove to be as diverse as the circumstances themselves. In other words it is impossible to give a universal answer that covers all cases.

At the end of the day we are mammals. Competing whether for mates or resources comes very naturally. Unlessss we are self aware enough to observe and correct our own behaviours, we will continue to behave in instinctual ways. I think tje instinct to quash a "rival" when the opportunity arises is very strong.

Prevention of possible violence when in real time. Yup it has been "That Bad" in my lifetime. But it is changing.

Here? Online? I hope others speak up. This construct is falling everywhere.

I suspect it may be a version of Stockholm Syndrome, the well-known phenomenon when kidnapping victims develop paradoxical feelings of affection towards those who hold them captive, even if they are subjected to cruel or violent treatment. It's believed to be a form of coping or survival mechanism subconsciously adopted by the victim in an effort to avoid punishment by forming an alliance with the aggressor.

all the thousands of years of forced submisiveness to man! Religions were invented to keep them and the poor in their place

Internalized sexism?

That's a damned good question, and something I've also been asking for a really long time.
I've never understood women who willingly (and often, gladly) throw their sisters under the bus for defying men and the patriarchy.
I've found it's primarily women who believe in gods. It's not exclusively them, of course, but it's primarily them. They are extremely resistant to anything that threatens their idea of the status quo, their comfort zones.
They'll demonize anyone who makes waves. They'll go out of their way to eliminate anyone they perceive as a threat.

That's as close as I've ever gotten to an explanation. I couldn't even venture a guess as to a solution.

Security. Or should I say perceived security?

i have not noticed women attacking women who stand up to men. my female friends support women who stand up to men (and so do i), assuming you mean standing up to men who are bullying or otherwise oppressing them and not just arguing with some guy who may or may not be right about whatever issue is being discussed. on what do you base this observation? it is the opposite of my own observations.

g