Mom is obsessed with world issue such as this war that Putin started, government taking away our freedoms and religion demise. Any ideas?

Put her in a facility. If she refuses to take her meds and is verbally abusive she cannot continue to live in your house

Block the news channels.

You say she is living with you due to a cancer diagnosis.
In your profile you say she has Alzheimer's/dementia.
2 things.
If she has dementia you can not reason with her.
Ask her doctor about medication to calm the anxiety.
If she has dementia, block the news stations she generally watches. Use some sort of reasoning that the cable service is down.
With the dementia you can not argue with her, you also can not have a normal conversation. So don't try. Change the subject, wear headphones or earbuds, earplugs, anything to quiet her rants.
Also look for some Adult Day programs so that she gets a break and you do as well.
IF the reason she is living with you is that she has cancer and is cognizant then you can tell her that you will leave the room is she can not carry on a conversation in a normal manner. If she starts in stop whatever you are doing and leave the room. (as long as it is safe to do so)
Again if she is cognizant you can tell her that is this continues she will have to find another place to live. You can schedule tours of Assisted Living places for the following day.

I'm not going to tell you what I would do but what I actually do. Like yours, my mother is obssessed with politics, cable news, and world issues. We also live together. She attempts at instigating fights with me about it throughout the day everyday. Here's what I do.

-DO NOT ENGAGE her! For a while she will double-down on her attempts to get you to fight with her about something. Learn the following response and repeat it as often as you have to:

There's nothing I can do about it and I will not discuss it with you.

Then walk away. When she sees that she will get absolutely ZERO attention from you and that you completely ignore her (and I mean totally ignore like she isn't even there), she will stop.
It will be hard for you to do this, but you must.
- She has to be limited as to how many hours a day she's allowed to watch cable news channels or talk news shows. If you have to put parental locks on these channels, do so. It's your house. You do not have to tolerate cable news with the gloom and doom 24 hours a day. Tell her that cable news and talk news shows are no longer allowed in your house.Or they will be restricted to a limited amount of time per day. If she wants to remain living in your house then she will have to learn to live with a restricted amount of cable news or talk news shows.

My mother tries to pull the BS on me that I do not believe in Jesus Christ and that I'm evil.
I tell her that she forgets I'm Jewish. The 52" high-def tv she enjoys with the premium cable package that has all the channels is paid for by her VERY Jewish former son-in-law who I've reconciled with.
She's hated him for more than 20 years yet he's never been anything but the very picture of kindness, generosity, and respect towards her. She even tries to engage him in some of the fighting and gets nowhere.
Take away some of the cable news and talk news. You'll be doing your mother and yourself a favor.

I would pull out Scriptures that are intended to give us peace and reassurance for the very times we are living in.

You can not reason with a broken brain but, you can open the Bible and read out loud to her and tell her that you don't worry or fret because you believe that all things are in God's control and according to HIS plan.

She is right, the world is going to hell in a hand basket. Try to give her The Word of God to help her not feel so frightened.

If you are not able to do this, perhaps you can set her up with a tablet. Alexander Scourby's audio Bible is on utube in it's entirety. She could listen to that.

Disable the news channels or the television set entirely. That's first. Second, if she's 'refusing' to do this that & the other thing, while living as a guest in your home, then she needs to become a resident in managed care where she's somebody else's problem entirely. Sorry/not sorry, but dementia often reaches a point where sanity leaves the conversation entirely and logic MUST prevail. That logic has to come from you b/c hers is gone now. This is not intended to be 'mean' or 'cruel', just to say that you can no longer manage your mother at THIS level of need, so allow others to do it now, and you go back to being the daughter instead of the caregiver. You go visit her on your terms and leave when the screaming starts.

Yes, times are hard and frightening. But an elder with dementia & cancer should NOT be focusing on such matters at all. Which is why medication is necessary for your mother if her religious beliefs are not going to give her the comfort she's looking for right now, via the bible or whatever. My mother was famous for saying she was a 'good Catholic' but never ever relying on God to help her through ANY crisis or fear she faced. I gave her rosary beads to help her get into prayer, nope. Books, a bible, nope. She just chose to live in fear all the time, even before the dementia set in, but once the dementia came into play, forget about it........then NO amount of logic or reason could possibly penetrate her mind and get through to her. Nothing worked. Except the fact that she lived in Memory Care AL and I could leave when she got too wound up. That and Ativan.

Wishing you the best of luck with a difficult situation. Please remember that YOUR life is important too. You are allowed to have peace and relaxation yourself; it should not be 24/7 about your mother and her issues.

She lives in YOUR home, right?

She lives there only if she gets help. Otherwise she needs to reside elsewhere.

Have you ever tried agreeing with her, i.e., "yes, mom, things are terrible. I can't see how this will end well. Maybe the US will need to invade. I guess we'll just have to wait and see."

Then leave the room.

She sounds like she has gone over the edge. Might be time to find her a nice Christain home and move her in.

Regardless of what you do she will continue to get worse; this is no way to live.

The ball is in your court.

My parents, who were married in 1933, would--were they still alive--tell grandma that the world was ALWAYS a mess. Just wasn't so in our faces repetitively as it is now. At 80 what works for me is turning it off. Honestly very little of it has an impact on me and mine.
I would sit Mom down and tell her that what she listens to, watches and etc is up to her. What she believes is up to her, and is best kept private to herself. I would tell her that her being able to continue to live with you in your home is DEPENDENT entirely on how much peace and joy and the love of life she can bring to the home. That you will insist on her moving into care if she continues on.
Much of how THAT goes over is dependent on whether Mom has entered the time of the loss of all inhibitions and control. If that is so, then the move is in order sooner than later. She has refused medications and all else you have suggested that might help, and there is no reason your own life should be sacrificed onto the altar of her angers.
To be frank (and you NEED TO BE AT THIS POINT) Mom has had her life. This is yours. Embrace it, and let Mom know that you won't let people into your life who don't keep it pleasant.
Period and full stop. People intent on making of each day a ruination should be kept farther away than an arms length.

Well, maybe start by limiting the amount of "news" she is exposed to? I would suggest cut back on viewing Fox, Newsmax and stations of the sort because they tend to get the elderly riled up. Also some of the "preachers" on TV and the internet seem to preach about how "religion is being persecuted", yet there they are yapping away for hours on end on various media platforms while raking in the $$$. That aside, is there a way for you to slip her psych meds into her food/beverages? I realize it sounds a bit outlandish and cartoonlike, but perhaps give it a try. Also, can you speak with her medical providers and explain that she refuses to take her psych meds? Maybe they can convince her that they are part of the regimen for treating her cancer...yes, mental health is part of overall health.
Good luck!!! It's very tough.