You deal with the people who MAKE and SELL arms rather than focusing on entire countries and having wars with them. You make it illegal to make and sell weaponry that it used to harm and injure people. You put in trade embargo, you improve world trade so people don't have to deal in arms and most of all you use the UN for what it is supposed to be for and bring people to justice who ignore the measures put in place.
Okay, let's work through that. We can only make it illegal to make weapons in the UK. All those other places have their own governments.
Ok so step one we destroy all of our weapons.
Now how do we force the others to stop? A Trade Embargo wouldn't work on any of the larger nations, but an embargo on the whole world could destroy our economy and millions might starve here.
It might work on governments of third world nations, but the worst ones will let their people starve before giving in - we've seen that before. Do you advocate that? Also to enforce a Trade Embargo means physical force unless you have the agreement of every single nation on earth.
You suggest the UN, but what can they do? Realistically they could send troops to enforce a ban on weapons, but they don't have an army of their own. It would be our army (and that of US/France/Germany etc if they agreed) and those troops would have no weapons under your plan.
It's like the recipe for Unicorn Soup.
It's really easy to make.
First catch a unicorn.....